i think it is a waste of money to upgrade the CPU for gaming. Do not bother yourself with CPU at all if you only need it for gaming.
Like I said previously, I have a Q6600 @ 3GHz and an i7 @ 4GHz and using a pair of 6870 they perform identically in games.
If you are gaming at decent resolutions then there is no point at all in upgrading the CPU because the bottleneck is the GPU. If you are gaming at low resolutions then a faster CPU will give you more fps but what is the point again if a modern GPU will already give you over 100fps?
it's a nice mobo you got there. throw in a couple of 6870 in crossfire and an SSD and you are all set for another couple of years. I am guessing your mobo can take a Yorkfield CPU with a BIOS update but you gotta double check that with someone who knows for sure. Again, I cannot stress enough how much of a waste would be any money spent on a newer CPU.