Very specific example here but i used Valley, which is as game like as benches get really. I think valley is threaded for four cores, which i suppose is a fair place to start thinking about CPU bottlenecks in games.
When i moved my GPU to my other rig, i benched it at different common clocks to compare.
[email protected] with a 290x OCed @1241/1500 Was scoring 25xx on Valley with the leaderboard's settings.
Same card with same clock was scoring 30xx in Valley when i put the card in my 4770k @ 4.4
Now in Valley my GPU usage is at around 99% when it isnt changing scenes, while it was no more than in the low 80's for my 8320.
I would look towards getting an i5, especially if you are going to dish out for a ud5 board. An i7 if you plan on Crossfiring eventually.