It is seriously cost prohibitive to "buy" a high end gaming rig. Most pre-built systems you find are going to either be under-powered or over-priced.
My humble suggestion : build your own PC component by component.
Just sit down and seriously consider how much money you willing/can afford to put into a new system, THEN consider your new build.
Get the best components you can fit in that budget. (seriously stick to your budget, you'll spend enormous amounts of money if you just keep adding "a lil more")
If you wanna pay $500 - $1000 dollars with a pre-built deal, go ahead but, don't expect any HUGE improvements and, you'll prob be wanting to buy a new one in less then a year.
Assembling a PC is fun and rewarding, and will save you tons of money in high end-systems.
