OP, Crysis is not single threaded, ABSOLUTEY NOT. There is a difference between a dual core and a quad core, tested this so many times back in the day, although it's an in-game set specific revelation. Crysis and F.E.A.R were the first gold standard games that made me a benchmarker in the first place.
Anyway, now that i thought about it, last time i played the original Crysis and the expansion was 2009 with my XFX HD 4870 512 MB, on a Core 2 Quad Q9550. On DX9 could reach 45 FPS at 1680x1050 resolution and with no AA whatsoever. That was ok. The previous HD 3870 scored a pathetic 22 FPS or something like that. There is actualy a report somewhere in overclockers.uk or in this forum. I have a 4K TV and always wanted to replay the game on that. Going to test this with my GTX 780, even though i have GTX 1080 Ti.