There's no official word from Dice or EA about the requirements for BF3. If it's similar to BFBC2 then yea, it'll get around 50-60 frames per second on max settings 1920x1080 resolution. As for Crysis and Crysis 2, not really.
You'll get roughly 30fps on max settings on Crysis and around 40fps on Crysis 2. It'll still be enjoyable. If you're going to spend that much money on the rig, you might as well SLI the GTX 570s (your board and psu supports it).
It'll definitely max any game that you throw at it on 1920x1080 resolution. Just make sure you get a quality 800w psu (OCZ, Corsair, Enermax, Antec, etc). Also, you don't need that much ram at all.
Gaming will only use about 2GB of your desktop memory and unless you plan on doing some photoshop editing, and stream some hq movies, and having 50 applications running in the background, you still probably don't even need 8GBs. I'd stick with 4GB and if you ever notice your mem usage at over 70%, then I guess you can always upgrade later, but it won't. By the way, your LGA 1155 board supports dual channel anyways, so unless you plan on getting multiples of 2gb or 4gb (if you really just want to get 8GB).
In the past "getting more ram" helped performance, but 4GB is more than enough for desktops. I'd spend that extra cash on a SSD drive which will turn your computer into lightning. Finally, this is sort of expensive (and you can upgrade this last), but I would suggest a good 120Hz 1920x1080 monitor.
It'll provide for less motion blur and it's a noticeable difference. Your computer will handle the games, but if your monitor is weak, then it'll be like watching a Avatar Blu-ray on a 720p instead of 1080p. Happy gaming!
Edit: Don't go for AMD cpus. The i5-2500k doubles the performance of phenom ii x4 965 BE cpu, and beats the phenom ii x6 1100T which is around the same price. If anything, he should wait for AMD's 8core cpus which is priced to compete against the 2500k and 2600k, but even still, I'd stick with the i5-2500k because gaming rarely uses over 3 cores.
I'd rather have intel's beefy 4cores. As for the i7-2600k, no. Hyperthreading doesn't help gaming (and I've heard it actually hinders it by up to 3%) because again, gaming doesn't use that many cores (processes).
Maybe in the future when games get more advanced, the 2600k can have an advantage, but until then, the 2500k is the best gaming cpu right now.
12gigs is overkill. 2x4gb kit is more then enough. Heck, 4gb is enough.
800watts, I don't know of a good psu manufacturer that make a good 800w psu, is it a GX800? Better options if you want to SLI ... 850w Corsair TX V2 , XFX Core 850w. You could drop down on the board to a gigabyte z68, unless you think you'll be using bluetooth and the uefi bios to the best of it's ablities.
Drop down in case. Step up to a GTX 580. BWAAAHHH!
Seriously though, the GTX 570 will max out those games, 8gigs is more then enough. Make sure the psu is 80plus bronze/silver.
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