I like to approach this from a different point of view. What do you plan to use this for? What games? Black ops is only dx9 so nothing demanding there. If you are going to play the new BF then thats on dx10. If you are going to play the new MMOs out then some are on dx11.
First of all you need to decide your PC ability. Are you willing to take the time to spend to tweak and stabilize your system. Is this within your abilities? Do you have to learn this? Are you willing to? If not or don't have the time then, a prebult is better for you. I would suggest having a game rig built for you. If you buy a brand name prebuilt then it is usually full of bundle crap and is locked out of any tweaking.
How long do you keep your PC for, 2 yrs? 10yrs?
If a long time then getting more than you need now that's expandable to accept upgrades later is best. X58 mobo are ddr3 with 6 mem slots that can handle up to 24gig ram that you will never use but maybe in future so its nice to have that option. Since win7 wants 1gig to run smooth and your game doesn't use more than 1 gig, you could get away with 2 gig of good ram if only gaming and fast processor. I rec min of 4 gigs for reg use. Try putting a ram meter on your desktop and see how little ram is used when game is running. I have 8 gigs and rarely runs 25% of it under heavy gaming and hosting.
When you are gaming are you also doing other things with the PC?
This makes how much processing power you need important. Extreme dual cores can rival quad cores if set up right. Quad cores are more than enough too run anything out there. An i7 quad has hyperthread that makes it run like a 8core which unless you are running muli apps or monitors or rendering, you will never use it but will be good for future. Same thing applies to 6 cores. I built an i7 930 w/HT on x58 mobo 1366mhz socket and 6gig ddr3 with 3 extra slots left open. Most of the time only 2 cores were even being used and ram was at 15%. It has a mid-range dx11 g-card but, this set up could add three more graphic cards, 18 more gigs of ram, could run multiple monitors in future. It runs a 1050 watts modular power supply that has power throttling to conserve when not needed, a very stable power set up.
Do you want to run a large monitor or tv?
This will be a factor for g-card and ram. the bigger you go the more you need.
Do you have good internet speed?
If you have a laggy net speed then no matter what, your system will stink. I run 62mbps dl and 20mbps ul. I don't have issues on my end and it's nice for hosting. It still sucks on other player end b/c it's then their slow speed that makes lag to me. A 15mbps net would be more than adequate if not sharing with others in the same house unless you are set as proprietary user. I know a lot of players have 7mbps or less and think it's fine, but they haven't run on higher to know the difference it makes. Get at least 5mbps ul also. The standard 1-2 mbps is min.
As for the liquid cooling, unless your are doing OC or extreme graphics you don't need liquid. I have gotten air to run very cold under high oc. Small fans are louder than large fans. 140mm fans move a lot more air quietly. The school of thought is if you have more processing and ram than you need then you don't have to OC. OC is to get more out of a system by putting the demmand on it. If you don't have the demmand then you don't need to OC. Don't skimp on the mobo in this case b/c higher end mobo are laid out better for air flow and have their own integrated surface heat disipation. I built a very high end expandable system for xrg member Chewy for $1500 that he will never fill to the max options. Learn to route cables professionally. Looks nicer and helps air flow.
The last thing that's important.
The hard drive. Not super important in gaming as if doing multiple apps or video editing etc where fast hd access is needed. If you are looking to the future and not doing all kinds of other crap, just gaming, and not multiple games (over5 installed) you could run a 150gig raptor 10,000rpm hd. They are pretty affordable now. Use a second larger 7500rpm hd that's cheaper to store stuff on instead of clogging up your main HD. If boot up time makes you wet then spend too much money and get a SSD hd. The thing with them though is unless you are demanding with those other apps or video editing most of time not noticable change.
