I've upgraded from an RTX 3070 and was able to play both Far Cry 4 and Company of heroes 2 at reasonable framerates at 4k. However, after upgrading to a 3080 Ti, I can only get 5 Fps at any setting on Far Cry 4, and Company of Heroes 2 is can only get 15-20 Fps at 1440p. I've switched to a different AIB (Asus -> EVGA) for my 3080 Ti and I'm getting the same issues. I tried Far Cry 3 for the first time with my 3080 Ti but got similar results as Far Cry 4.
 
Surprisingly, modern games like CP 2077 and Halo Infinite perform as expected.
Specs:
i7 4790k stock
16gb ram dual channel
1tb SSD
Asus Z97 sabertooth mark s.
1200W Evga P2.
Windows 10.
 
I have already tried wiping my drivers and reinstalling them via DDU, uninstalling current drivers and installing older drivers. Enabling Windows 7 compatibility does not do anything.
What is going on?
 
Thank you.

This is bemusing me - why are you trying to run a 4th Gen Intel with a 3080ti and also 16 Gb of RAM which i bet is clocked at 2400 MHz* as well (not to mention a 1200W overkill PSU). I'm going to go out on a limb and say it hasn't got anything to do with the performance of the GPU that's limiting your game performance..
 
The other thing to bear in mind is that, the Asus Z97 is an OLD Mobo as well and only supports PCI 3.0 NOT PCI 4.0.. 
 
*Edit: Scrap that it wont even be clocked that high as its DDR3 so probably 1600 MHz.. Your RAM is 100% going to be a bottleneck there, particularly if you are trying to run games in 4k on a large monitor. 

Hmm, doesn't seem like the 4790k would cause Far Cry 4 to run at 5 fps.  Initially I had my 3080ti FTW3 running in a 4790k machine.  It worked reasonably well and generally only bottlenecked badly at higher framerates. 
 
OP, when one of the games like FC4 is running at such low framerates, what clockspeed is the core running at?  Use GPUZ, PX1, etc... to monitor the 3080ti.  Post a screenshot.
 
My first guess is the card is just idling.  I've see this all the time in the menu's/map in GTA5.  Alt tabbing out of the game and back fixes it for some reason.  This has come up before on this forum, but I don't recall if there was a better fix.

I ran into something similar on Bioshock. The game doesn't put enough load on the card to keep it in it's correct power state. Ended up dropping to like 200MHz and then jumping around a lot.

Windows performance mode and then maximum performance mode in Nvidia driver settings fixed it for me. It won't down clock below like 1800MHz though so it's constantly pulling like 100W or more doing nothing. You'll want to use a frame limiter as well in the Nvidia driver or in game. This also fixed light stuttering I was getting in AC Odyssey as well.

moldy cheese
I've upgraded from an RTX 3070 and was able to play both Far Cry 4 and Company of heroes 2 at reasonable framerates at 4k. However, after upgrading to a 3080 Ti, I can only get 5 Fps at any setting on Far Cry 4, and Company of Heroes 2 is can only get 15-20 Fps at 1440p. I've switched to a different AIB (Asus -> EVGA) for my 3080 Ti and I'm getting the same issues. I tried Far Cry 3 for the first time with my 3080 Ti but got similar results as Far Cry 4. Surprisingly, modern games like CP 2077 and Halo Infinite perform as expected.Specs:i7 4790k stock16gb ram dual channel1tb SSDAsus Z97 sabertooth mark s.1200W Evga P2.Windows 10. I have already tried wiping my drivers and reinstalling them via DDU, uninstalling current drivers and installing older drivers. Enabling Windows 7 compatibility does not do anything.What is going on? Thank you.

Try *disabling* Above 4G Decoding in the MB bios, if you have an option for it.
 

03whitegsr
I ran into something similar on Bioshock. The game doesn't put enough load on the card to keep it in it's correct power state. Ended up dropping to like 200MHz and then jumping around a lot.

Windows performance mode and then maximum performance mode in Nvidia driver settings fixed it for me. It won't down clock below like 1800MHz though so it's constantly pulling like 100W or more doing nothing. You'll want to use a frame limiter as well in the Nvidia driver or in game. This also fixed light stuttering I was getting in AC Odyssey as well.

 
And this.  Set a profile for each game in the Nvidia Driver.  It's the power state setting.

Hi thanks for the responses everyone. I will post a screenshot of GPU and CPU utilization shortly.
 
With regards to the Nvidia control panel setting, yes it has already been set to maximum performance.
 
The reason why I haven't upgraded my CPU and mobo yet is, as we know, things are getting interesting with intel and AMD cpu releases and was hoping to hold out until then. However it looks like I will have to upgrade if and will update you guys if anything changes later.

That game ran fine at 1440p on Ultra settings with my GTX 1080ti, before I moved it from i7-3770k to my i9-7920X. It's not your CPU at all. Especially since it ran fine for you with the 3070. Likely going to be fixed by a setting in nVidia Control Panel, under Manage 3D Settings -> Program Settings. 
 
Personally, I would try DSR setting tweaks to make the game render at a higher res, and then increase the resolution in the game. That should force the card to work harder, which in theory might solve your issue. Downclocking might work too. Some of the settings are Global-only. You'll have to fiddle around with them to figure out which works best for you.
 
For limiting frames, the setting you want to tweak in nVidia Control Panel is "Max Frame Rate." I've had to use that before to solve not just stuttering, but intermittent hangs/freezes in games that would last upwards of 10 seconds each time it happened. (That almost drove me nuts.) "Max Frame Rate" to the rescue for that one.