Hi :)
 
TLDR: will a 360 and a 240 HWLabs Nemesis GTS be enough for a 6800k and 2 GTX 780 Ti's (or equivalent TDP cards in the future) ?
Fan setup will be Push only on the 360 and push/pull on the 240.
 
It's been a while since I was last around, been to busy with enjoying my rig and real life and stuff. Time has however come for me to upgrade my pc and in this upgrade I have decided to finally go over to the dark side and drop the thing under water.
The planned parts are currently:
Intel i7 6800k on a EVGA X99 FTW K and a single GTX 780 Ti(but will likely expand to a SLI setup at some point)
 
My case(a Fractal Design Define XL) is a little problematic, as it was never designed with watercooling in mind, and while I could replace it with something more suited, I like it a lot and think it would be neat to watercool in it. Some modifications will be necessary to accommodate the watercooling parts and space will be at a premium.
Having meassured it out, the best I can fit is a 360 and a 240 with a maximum thickness of 30mm. I have already gotten a hold of a HWLabs Nemesis GTS 360 and really like the build quality, so I will be ordering a 240 of the same series.
 
Now if I have already decided which parts I'm going with, why ask? Well, I like knowing the boundaries of the parts so I'm a little more prepared and can plan ahead better. If for instance you guys unanimously tell me that the rads won't have the heat dissipation necessary to keep 2 cards and the CPU at an acceptable temp, I can plan ahead and buy the strongest single card I can get my hands on within my budget instead.
 
Thoughts?

You should be good to go there.  Just make sure with your modding you have enough air intake to counter the exhaust.
How are you orientating everything as far as intake and exhaust.  It is true for cooling in general, but even moreso with water, you want positive case air pressure.

I suggest removing the middle partitioner and the 5.25" bays if you don't have any 5.25 devices, it really opens it up. You can fit a 360 rad in the front that way, albeit a bit awkwardly.
360+240 is plenty though, you could do 3 gpu's + the cpu if you really wanted to and still maintain great temps.
 
As for the air flow setup, 2x front intake + 1x rear intake + 3x top exhaust should get you the best thermals.