i would definitely go with an hd6870 in this budget range. the gpu is going to be the limiting factor for almost every game, this is where extra money leads to extra fps. id grab the sapphire bundled with 8gb of ram: http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...
ram is so cheap right now its silly not to go for 8gb
a 2500K on an H61 is wasted money . The advantage of the K is that it can be overclocked so using it on a mb that cant OC is nuts IMO . Especially when you consider an oem windows install will be locked to that mb , then updating is harshly expensive
Better to get the Z 68 mb
The OPs budget has some head room though and if he's willing to spend the whole $600 he can get an i5 2400 and a better graphics card . The 6870 makes sense . Search by price
I know I could make a build with a 2400 and a 6870. But I personally would rather spend the money on the case, as stupid as that sounds because I am not a hardcore gamer so I would rather not waste the money on stuff thats overkill.