I looked into that Dell computer you listed and with its specs I could build something with near identical performance including windows for $870. http://pcpartpicker.com/p/PNbDsY
The big catch is that the 4GB NVIDIA GeForce GTX 745 Graphics card is specially made for Dell and its performance is on par with mid range cards that came out in 2012 despite the 4gb. So GPU would be a major bottleneck for this rig, which for normal computer would be fine but the worst thing you can have for gaming and graphic rendering.
Because at this point I build them myself rather than buy prebuilt I don't have a good suggestion for where to buy prebuilt, but places sites that build custom gaming computers allowing you to specifically pick each part (including cooling, case, power supply, etc.), such at the one you used, is probably your best choice.
» Edited on: 2015-07-09 12:47:26