Sry if i got you all mixed up with the bottle necking thing. However it seems like you want to most from what your spending i just see it as a waste to spend money on something you cant fully use. However if you do by a high end gpu it will still be blazing fast but not as fast as it could be. I just wanted to make it known that you wont being using everything its got. But if your going to slowly over haul your rig the gpu would be that 1st thing to trade out just make sure your 12 volt rails have the amps needed. I tried to read all the posts before my last one but i hate reading so i just skimed them kinda got the idea. Did you post your full system specs? X2 5600+ i saw what kinda mobo is it a am2+????? or just am2
*EDIT*
have you looked at any gpu benchmarks? However i dont know what the rest of their system specs are they test these with i can only think its something crazy and completely overkill. Have you thought about crossfire or sli? can be cheaper sometimes.
http://www.videocardbenchmark.net/high_end_gpus.html
