No to liquid cooling. Either one of those video cards will get the FPS you're looking for paired with either an Intel or AMD 3 or 4 core CPU.
You would get a bit more performance with Intel and pay a bit more for your overall system.
AMD would give a similar if slightly slower gaming experience, but shave a few bucks off.
You can use ddr3 with either AMD or Intel. The only reason I see for going with the more expensive i7 would be triple channel memory VS dual channel. Also I am unsure of 6 core upgrade path for p55 motherboards, but would assume as with the AM3 that there will be processors available later this year.
As whitefang mentions, it is helpful to know budget and so forth. You should follow the sticky under new systems in the forums.
Total: $1,157. This is be overkill for your resolution. However, if you were to get a 1920x1080 monitor, it would still play every game with maximum details.
Crossfiring right away is not a good idea. Especially since you're using the older generation of cards. You'll want to replace the 4870s in a year or two and then you'll just have wasted money. Not only that, but a single 5850 or 5870 would be better than the two 4870s.
Most balanced and sensible build mock-up yet in this thread, in my opinion. Even though I'm not crazy about the Biostar and OCZ picks! But that's just personal prejudice... But since the OP won't be OC'ing, the higher clock speed of the Phenom II will pay off for him in those apps/tasks that are CPU bound, and with a 5850, the games won't really care what kind of proc he's running. Now, all that said, if it were me and I had a budget of $1,200, I'd definitely go i7-930. But that's because I'm an obsessive power user who vainly cares about keeping up with the PC Joneses. I always feel compelled to have a better rig than my friends, but now I'm lagging behind and I can't wait to stick it to them with a new i7 build! But back to the topic... There's also the larger picture of the platform as a whole - using the x58 chipset would definitely be better if you plan on using multiple GPUs in the future, but the AMD 890 series chipset is the better choice if you really do care about getting the most out of SATA 6G and USB 3.0, due to it's native support. So as always, it's a balancing game.
The X4 955 may have a higher clock speed, but the i5-750 is faster. Also, the i5's turbo mode makes it drastically faster for gaming.
Sorry, dude, but I have to disagree. I've seen plenty of benchies on both procs, and it's rare for the i5-750 to beat the Phenom II by more than 5-10 frames or so. And that's at framerate levels where the gamer wouldn't be able to perceive a difference anyway. The notable exception that I can think of would be Far Cry 2, but for the most part, and in the vast majority of games (including Crysis, which the OP referenced), the Turbo boost isn't offering much to speak of when it comes to playing games.
I don't know what benchmarks you're looking at. The i5-750 is drastically better than the 955, with few exceptions. There may be a few benchmarks (mostly productivity ones) where they are about the same, but the i5 is better in gaming period.
The i5-750 wins in the following: Left 4 Dead, Fritz, and FarCry. The basically tie in GTA 4. Those are the only ones listed in the charts, but I know it does better in pretty much every game.
Problem with the i3s are that they're more expensive than the AMD solutions (counting the cost of the boards) and worse than the i5-750. So they fit in the budget in between the two choices (X4 955 and i5-750), but aren't really the best choice for either.