I was looking to upgrade from my 8800 gts 640mb to either the gts 450 or the gtx 460. my question is that the 450 has 192 stream processors while the 460 has 336, would i really notice the performance difference in 144 more sp. Also about the memory interface, one is 128 bit and the other is 256 bit, would that be much of a difference. I was wondering because if i do get the gts 450 i would probably try sli because it wouldnt be that much more than the single gtx460.
Shaders are similar to cores on a cpu, but even more effective because alot of applications run today are single threaded, using only 1 core, whereas gfx is a parallel application, which can use many shaders (cores) at the same time
Also, just like 1 cpu isnt like another, as the cores change, so do the shaders.
The bus width, or 128 vs 256, simply means how much data can be moved within and out of the gpu, similar to a hose and water
Having a larger hose doesnt mean its faster, unless you have more pressure (more and better shaders etc) pushing it
Stream processors a.k.a "Cuda Cores" are the main part of what gives the Nvidia cards their oomph after that it's clockspeed, memory interface and RAM amount so a GTX460 1GB with the 256bit interface is the one to go for.