Perceived bottlneck will be nothing i bet everything looks better than before. However in reality the CPU is likely holding the GPU back from its full power. Can you max out your games though? If you can then really who cares its doing what you want and can be carried to your next build most likely.
the 640 isnt the greatest quad but if you can get it to 3.2 or higher you shouldnt have that much in the way of a bottleneck... maybe 7-10%
the higher spec gfx the game has the less chance of bottlenecks showing but you may get huge fps drops in games like bf3 as the unbalanced nature of your pc will show on apps that require 2 or less threads... this is probably where the card will overwhelm the cpu but turning up aa or adding a serious oc then you should be able to get it under 5%
to get the best from that gpu you really do want 1 of the faster most powerfull quad core amd offer like a 960t, but even then your still likely to have some performance issues.. anything less will give more and more issues as you get lower down the power scale...
so i would say your likely at the very limit of what your cpu can handle...
My friends Athlon II X4 630 was holding back his Radeon 6850 in some games, and that was at a resolution of 1600x900. He saw improvements moving to an I3 2100, his reason for upgrading was to get better performance in that new Star Wars MMO.
Your not terribly bottlenecked, but there would definitely be improvement in games with a better processor.