Your intended purpuse, Gaming only, is going to be determined more so by the dedicated GPU that you buy. For purpose of "future proof" and not Kicking yourself in the Hind quarters later - I'd recommend the I5-2500k and a mid level P67/Z68 Board. The diff between the I5-2500 non k and the K is ($10) just not enough to recommend the Non K unless going for a H67 MB then I'd go with the I5-2300 (still only 35$ cheaper.)
I'm sure from the previous posts in reference to the Dell - DON'T. not with standing the Reliabilty issues, that system is for Kids using $10 Kids games or for email and internet broosing.
On MB. Most Mid level P67 boards will do, myself I prefer the Z68..
..If you will NOT SLI/xfire, don't sweat the Nr of pci-e 16 x slots.
..Do look at the distribution of the SATA II/III ports - do they Support your current and Future needs.
..USB3 port - # of USB2 and USB 3. Most should be OK but verify.
..Pick a board that has a relative High number of people who have commented on the board of choice (newegg) and has a Low dissatifaction ratio (ie 1/2 eggs rating) - bear in mind that these need to be taken with a grain of thought.
Personal experience: I bought the ASRock Z68 Board for I5-2500K. Like the board, would be great for gaming if going SLI/Xfire (Has 3 PCI-e 16x slot (8x,8x,8x if all three are populated. . OCs very well. BUT I should have paid more attention to the Sata II/III ports 2- SATA II, 2 Intel Sata III, and 2 Marvel Sata III.
My real requirements - 2 SATA II Optical drives (one Blu-ray Plus one DVD) and 2 Sata II HDDs and 2 SATA III SSDs. Will probably put my 2 SATA II HDDs on the SATA III marvel controller. Excellent USB2/3 distribution.
For $120 - Great price, good reviews for card in this price range. Normally do not recommend sub $100 MBs
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157251
This is a Z68 MB (Like combining a H67 and a P67).
.. I perfer the Z over the P as it allows you to build and TEST the system without a dedicated GPU. Should you have a problem with the GPU down stream you can always use the HD3000 IGP (Not so good for gaming). The Other advantages you would not use.
.. Only disavantages - (1) limited PCI-e slots, only 1 x16 and 2 x1 slots. This limits the MB to a single Graphic card and limited added on cards such as audio cards (the audio card would have to be pci-e x1, or older pci card). (2) probable would not support a HIGH OC, mild OC -OK.
PSU - do get a QUALITY PSU ( do not jeperdize your investment).
.. For Single card like 6770 and I5-2500k Non OCed a Quality 450W Min -> 650 W would be a good choice. The 650 would cover a higher end GPU and an OCed CPU.