turn off realtime reflections and toggle the occlusion culling and shadow lod settings.
also turn on the (lod) setting.

a 560 is in most cases more powerful than a 645

http://www.game-debate.com/gpu/index...eforce-gtx-560

numbers to look at

Pixel Fillrate
Memory Bandwidth
Texture Fillrate


FTR, what exactly burnt in the old rig? and how?

my 920 is still going strong overclocked to 3.8 after all this time.