I presently have a GTX 285 on a Core 2 QUAD (Q9550@3GHZ) system, with 4GB of DDR2 (800MHZ)memory, on XP. Would it be worth me upgrading the GPU to a GTX560ti, and selling my 285 on ebay?
Check out the comparisons. Sometimes the increase in performance is substantial, other times minute. But in every case (even power consumption and noise level) going to the 560 makes sense.
I could not find direct comparison between them but GTX 560 TI is on average 5-10% faster than the GTX470 http://www.techpowerup.com/reviews/ASUS/GeForce_GTX_470/30.html so it would be about 25+% increase + newer tech. Whether it is worth it you will have to answer it yourself!