Ok well, under the assumption that you aren't out there to reach the best 3dmark score you can.
That computer looks overpriced for no benefit. I mean, a hard drive cooler? come on. Overclocking hardly nets you anything anymore in terms of performance. Long gone are the days of OC'ing your 486 to DOUBLE your frame rate. Shortening the life of components for an extra 2fps when you are already pushing out more fps than your monitor can handle is silly.

Ok rant off.

Here are my suggestions that could save you a ton of money, and net you the exact same real world performance. (I consider it improved performance due to quad monitor output)

Case: Your case is going to be a big. A full tower is a monster. You aren't stacking it full of drives, and nothing you have needs that much space. However Antec is a really good brand. You could easily go for the 900, and get the same case in a smaller form factor. If you want something that won't be as loud as the 900, there is the P180/182. (I personally love the P182, just picked up my second one for $80 on sale ) Save $50 by switching to the 900. You won't need extra fans. Save $13.58.

Processor: Very few things you do will be bound by the processor power. However, I think the processor you chose is fine.

Heatsink: Core2Quads have very low thermal output to begin with. In fact most people can easily reach 3GHz with the stock heatsink. (Thats what made the Q6600 with G0 stepping famous) Don't buy a heatsink. In fact I recommend you don't even OC, but thats your call. Save $29.99 not buying a heatsink.

Motherboard: Hmm, you chose an nForce motherboard with an ATI graphics card. Unless it recently changed, you can't xfire with nForce. Only SLI (if I am wrong someone please correct me.) Since I see below that you seem to want DDR3 I'll run with that. Here is a Gigabyte board that supprots Xfire, DDR3 (even at speeds faster than your procs FSB, so if you want to tweak it you can go out of sync with FSB) I personally love Gigabyte boards, and highly recommend them. $149.99 Gigabyte MotherBoard. Save $186

Power Supply: Well, I don't think you need that whopping powersupply you have. 1200 is a LOT. If you follow my advice below on video cards, I say you could easily get along with something thats provides 1000 (even less if you really calulate it out, but ATM I cannot access my video card power draw chart., being at work) Here is a 1000W 80% Plus Powersupply from Antec. Its $179.99 saving you $50 (even more on your powerbill).

Video Card: Ok, here is where I really hope you heed my advice. The 4870x2 is cool and all, but it scales horribly. If you look at these benchmarks you will see that 2x 4870x2 cards actually perform no better than 2x 4870 cards, or a single 4870x2 for that matter. So thats an extra $489.99 for ZERO benefit it you run them crossfire. Since you are looking to go multi(3+) monitor output, I suggest going with TWO 4870 cards. This way you can enable crossfire when you want to play games on one screen, and get the same performance as your 4870x2 card. Then when you want to multibox you can disable crossfire, and run on all three monitors. I strongly recommend going with 2x 4870's. $200 each. Thats $400 for both cards. Save $89.99 and gain up to 4 monitor output while maintaining the EXACT same performance as both a single and dual 4870x2's.

Memory: You will not get any better performance using 6-6-6-20 RAM vs 9-9-9-24. RAM is not a bottle neck. GPU is the main bottleneck in gaming (processor sometimes). RAM only comes into play when you don't have enough of it. If you have to access your hard drive, then you will be bogged down. You won't be able to tell a difference between different speed RAM. Unless you are running a memory test program, you won't even be able to measure it. I suggest you save some money by going with some looser timing ram. G.Skill makes a 4GB set for $95 I would go with two of these, to save another $100.

Your Hard Drive/OS/Monitor choice are fine. (Nice monitor BTW) Just toss that fucking hard drive cooler to the wind.

So that right there is $518 dollars saved. Hey look, enough to buy two extra monitors and guess what. Now you can output to all three of them. YAY!

Hope that helps.