What is your priority playing with hardware or stable gaming with high graphics?

If it's gaming I would try and keep things simple.
No overclocking, and avoid multi GPU setups. This also simplifies motherboard options.
Now is a pretty good time to build simple powerful XP builds as CPU and LGA1155 motherboards are obsolete but still plentiful.
I'll leave specific video cards to someone more knowledgeable with Crysis.

Personally I'm more about the hardware so have systems dedicated to SLI or Crossfire but I also know these systems are far from ideal.

Never mess with any Crossfire or SLI if you just want to play your games. If you want Crysis to run more or less stable, you'll need something with GeForce GTX 580 level of performance.

I am no stranger to dual gpu set ups I do know that they introduce hitching and stuff this current build I fried was a 9800 gtx+ sli which I had been running for at least 10 years now and I could get pretty decent fps in Crysis with it. This new pc I bought I missed the fact that it was not sli ready so now I am down to one 9800 gtx+. I would like to replace the gpu with another nvidia that can perform similarly to the sli setup I was running. I am having a hard time finding definitive info on which card would be a good choice. Now I was going to go with a rtx 960 just cause that is the last whql driver for xp but since I only have a qx9650 it seems like that would be a steep bottle neck for my cpu. I don't want to drop 80ish dollars and only be using 60 percent of the gpu power when I could have gone with a 20 dollar card and get the same performance. The best info I found was maybe a rtx 460 is a good match. I do love performing benchmarks and ocing and squeezing out ervery last oz but mainly I want to play my game collection highest res all eye candy on with max fps. I am on a crt 1280x1024 for most every thing.
Yes I have seen 1155 systems really affordable but I am going for some what era correct. I just picked up an old lenovo desktop and it had a i7 4790 so when I can source a mobo for that one I also have a amd 7970 laying around could be a fun machine to mess with.

Just my experience

My main XP rig is a single X3320 with 2 GTX590's
My main Win7 rig is a dual X5504 with a single GTX 780

Admittedly hardly any of my games are SLI aware but in my experience it does just as good as the 590's

The XP rig could probably do with a CPU upgrade but none of my XP era games require it, In fact none of my XP era games require such powerful GPU's either. Instead I use the excess power from the GPU's to set AA,AF, etc to the highest settings.

I did have a pair of AMD 7990's in the Win7 PC for a while but could not get them to work in XP which was important for me which is why it now has a GTX 780

Crossfire is represented by a pair of HD 4890's in a dual X5460 system but that's not in the same league as the 2 above.