First of All, Welcome to the Wonderful World of Sub-Zero Cooling.
 
And Yes, Getting the Temperatures on the GPU(s) to -40C would DEFINITELY be enough to increase the Overclocking capability of Graphics Cards, and Over the Years here on the EVGA Forums, I will say I have tried Everything from Chilled Air Cooling through Dry Ice Cooling on my CPU's/MB's/GPU's in my Quest for "Getting it Colder".
 
Presently I have been using a Custom SS Phase Change (and occasionally Dry Ice) for CPU Cooling and a Custom A/C Conversion Water Chiller that is "Capable" of reaching sub-zero temperatures for the Four Titan X Hydro Coppers on my Benching Rig as shown in my Mods Rigs.
 
While my 300W SS will reach -40C at the Evap Head, Under Benching Loads, The ASUS OC Panel will show that the 5960X running at 4.875 GHz will produce enough Heat to raise the actual CPU temp anywhere from -11C to +20C during the Benchmarking Run.
 
The Four Graphics Cards use +15C to +10C (or Colder) Chilled Pure Anti-Freeze  for GPU Cooling maintained around +20C to +16C Temp measured by EVGA Precision X software and those temps can be adjusted Much Lower depending on other factors such as the Humidity/Temperature of the A/C Room they are running in, But I always adjust my Chiller to Just Above Freezing to prevent too much Condensation from forming.
 
I will add that my Chiller uses a High-Flow submersible pump (actually Two) to help keep the Cooling Liquid Medium from Freezing-up (when running near sub-zero) inside the Hose Lines/Water Blocks due to Physical Flow restrictions in my 4-Way SLI Cooling System. 
 
Using this Overclocking/Benchmarking Rig setup I have managed to get some Top Ten Futuremark HOF Scores while STILL being able to run this System 24/7 If I so desired.
 
I have used sub-zero liquid Cooling setups in the Past, So If you are Planning to go sub-zero using a Water/Alcohol/Anti-Freeze medium, You will find that even if you Insulate EVERYTHING (Hose Lines, Graphic Card PCB's, etc...) to prevent Condensation from forming and Shorting out Components, There will Still be a point where Frost/Ice will be impossible to prevent, Not to mention the amount of Water produced when you turn the System Off and Everything Thaws Out!
 
I have experimented with using a Modified-to-Fit SS Phase Change on a Single Titan X Graphics Card that did manage to maintain around -12C to -16C while under Benchmarking Tests with favorable results, But unlike the EVGA Full Coverage Water Blocks, this only Cooled the GPU and Not the Memory or VRM Chips and also would be impractical for more than Two Cards (Space Limitations between the Cards) including the requirement of an additional SS Phase Change Unit which means there would be THREE SS Phase Change Units in this particular Rig (One for the CPU, Two for the Graphics Cards).
 
To my knowledge, The only other way to run your System at Near -40C and Lower sub-zero temps on the Graphics Cards is with the use of Dry Ice or LN2 using Pots attached to the GPU's, But this is not a "Turn on and Forget about it" method of Cooling that doesn't require CONSTANT Temperature Monitoring and Coolant Level maintenance.
 
I'll just say that if you DO decide to go ahead and use Sub-Zero "Water" Cooling on your GPU's, It will be an Experience you will not soon Forget, But Then Again.......That's where the Fun Starts!

 
     

   Hi, JameshyB46, Welcome to the Forums.
 
I had posted that reply 5 years ago to this very Day! Hard to believe it was that long ago.
 
In answer to your question about the possibility of sub-zero cooling ALL the system components using multiple Phase Change units, I know back in 2006, the CPU and one or two Graphic Cards in the past have been sub-zero cooled using a HYDRA triple head phase change unit for the CPU and two GPU's. Originally Sold by FrozenCPU.com, That unit has been not available and out of production for quite a while.
https://www.techpowerup.com/11804/cooler-express-hydra-sli-phase-change-triple-evaporator-now-available
 

As far as sub-cooling the rest of the components (VRM, Chipset and ram memory), It would probably not be needed (plus would be very difficult to accomplish) and more than likely the sub-zero cooling effect of the two graphics cards and cpu would produce passive cooling to them. 
 
 

Unfortunately, The 2006 Hydra was the only dual GPU/single CPU phase change that I know of. 
It was really just a large single stage phase change unit that had three separate evaporator Heads attached to the same evaporator line.
 

 
You could build your own (or possibly have it built for you) by modifying/connecting two GPU evap Head lines and another single CPU evap head line to a fairly large single stage phase change to duplicate what the Hydra was like back in 2006.

A water chiller can get to sub-zero temperatures, But at sub-zero temperatures you have the problem of Lots of condensation forming on the chiller lines.
Since 2008 I have been using my A/C Conversion Chiller on my CPU and multiple GPU arrangements (2, 3 and 4-way SLI setups) with the ability to adjust/control the temperatures just to the point of not having condensation form on my chiller lines while only using the computer for web browsing and occasional gaming.
Only when I am Overclocking/ Benchmarking do I go sub-zero.
 
 

With my present new build I have an ASUS ROG Zenith II Extreme / AMD Ryzen Threadripper 3990X 64-core that is temporarily using two ASUS GTX 1080 Ti's in SLI until the release of the EVGA RTX 3090 Kingpin. 
Even using outdated Graphics Cards, I have still managed to get to #8 in the 3DMark Time Spy Extreme CPU Score with my AMD Ryzen Threadripper 3990X on Chilled Water Cooling.
https://www.3dmark.com/spy/14136437
 
The present CPU and both GPU's are on Chilled water using my 6000 btu A/C Conversion Chiller that has been operating since 2008.
My previous build was an ASUS ROG Rampage VI Extreme Omega / Intel i9-9980XE / Two EVGA RTX 2080 Ti Kingpins that were also under my A/C Conversion Chiller and in July, 2019 I was near the top ten in 3DMark Time Spy Extreme, But since the release of the 30xx series, I have dropped to position#53.
 https://www.3dmark.com/spy/7827302
 
My home-made Chiller (pictured in my previous post) originally cost me around $400 to build and is still much cheaper than the $2000+ units that are available today, But then that is just my preference.
I am sure that the newer chiller units will reach lower sub-zero temps than mine and it all depends on How Much you want to spend to achieve your goals.
 

Ok, now with the phase change I assume I wouldn’t be able to use a full coverage GPU block am I right?

Here is some 2008 photos about a Hydra-Type build by Biohazard that shows how he adapted the two GPU's into the single CPU evaporator line.
 
https://www.techpowerup.com/49582/biohazard-showcases-phase-change-cooled-system
 

Thanks guys for giving such great updates on the state of ss and chiller cooling. It seems so bizarre to me how 24/7 sub-ambient fell of the face of the earth so hard, what with TDPs rising so hard every gen recently. The community seems to have hard pivoted to only water-cooling or ln2 as considerations with chiller a niche, ss a super niche, and cascade the giga niche buried at the bottom. 
 
Anyways, can anyone point to any DIY chiller and/or ss phase cooler guides besides the ones from our illustrious TiN? His are fantastic, of course, but more reference points is always helpful. 
 
 
 
 

This is pretty awesome. I'd love to try to build something with phase change at some point.

If anyone is interested in getting a custom phase unit or chiller built in the USA there is an active custom builder that hangs out on Discord. He goes by the handle "mythical tech" and can be found on the Discord server linked below. The appropriate channel to discuss in is #subzero-overclocking. Feel free to message me if you would like me to make an introduction. My handle is Doomed83#9672
 
Discord invite: https://discord.gg/sj3dpxJ

johnksss

Doomed83
If anyone is interested in getting a custom phase unit or chiller built in the USA there is an active custom builder that hangs out on Discord. He goes by the handle "mythical tech" and can be found on the Discord server linked below. The appropriate channel to discuss in is #subzero-overclocking. Feel free to message me if you would like me to make an introduction. My handle is Doomed83#9672
 
Discord invite: https://discord.gg/sj3dpxJ

Where is he located at?

He is located in the Northeast unfortunately.

johnksss

Doomed83

johnksss

Doomed83
If anyone is interested in getting a custom phase unit or chiller built in the USA there is an active custom builder that hangs out on Discord. He goes by the handle "mythical tech" and can be found on the Discord server linked below. The appropriate channel to discuss in is #subzero-overclocking. Feel free to message me if you would like me to make an introduction. My handle is Doomed83#9672
 
Discord invite: https://discord.gg/sj3dpxJ

Where is he located at?

He is located in the Northeast unfortunately.

Unfortunately northeast means nothing to me at the moment, sorry. How about a state maybe?

Last I knew he was in Vermont, but I think he might have moved to Virginia.

nice thread and nice pics.