7770 2 gb vs 6850 1 gb

The performance is more or less the same however the 2GB will serve you better if you play on a high resolution or multiple screens. Also the 7770 consumes less power and (I think)is cheaper

the 2gb wont serve you better across multiple screens because either of the cards cant cope with modern games across multiple screens. both cards are a bare minimum for 1920x1080 gaming, more than that and you really need more power. I would strongly suggest spending a lot less on the CPU and spend a lot more on the graphics card for a gaming machine. Buy one of the lower end i5's. also, dont buy a cheap psu unless you want it to explode taking the rest of your pc with it when it does. A good quality well respected brand 500w psu is plenty.

Yeah, 1gb should be fine, unless you're doing some serious AA/Multi-monitor then you'll probably need 2Gb, but otherwise, 1gb will work fine for 1080P.

Get a cheap PSU, but not a crap one, get one that's well reputed, like OCZ, I hear they have really great budget models, also Antec and Corsair to name a few.

Also, you might want to buy some of your own thermal compound, such as MX-4 for your i7, since the new IVB CPUs come with crap thermal compound on the stock heatsink, causing higher temps.

Edit: Misread the graphics cards; I agree with crowe, you should probably focus on getting a higher-end graphics card. The ones you listed will probably struggle to play modern games, I suggest a 7850. From what I've heard, those in crossfire are really great.

the new ivybridge comes with crap paste between. the die and the heatspreader. there's nothing yih can do about that, that's just Intel sabotaging their own CPUs. whatever's on the actual heatsink should be fine unless overclocking, and then you need a different heatsink anyway. There's no reason to buy an i7 for gaming. an i5 K and a 7850 are a much better match