You and I must have done the same research. I went out and bought the GTX 560 Ti yesterday, $205 CAD after a $35 rebate. Only 1024 MB video memory. I replaced a GTX 285.
Using John Cline's Rendertest 2010 (minutes:seconds):
V10 3:34
V11 GPU off 4:17
V11 GPU on 0:52
So about 4 times faster than V10.
Timeline playback (fps) of Cineform clip 1440x1080 60i in a preview window 912x513x32 with Magic Bullet Looks skin smoother preset and Sony Gaussian blur - light blur:
V10 Preview auto 28
Preview full 3.3
Best full 1.6
V11 GPU off
Prev auto 28
Preview full 3.3
Best full 1.6
V11 GPU on
Prev auto 29.9
Preview full 13
Best full 7.5
So the 560 Ti gives about 4 - 4.5 times more fps in Preview full and Best full.
I've just started downloading Sony's 2.5 GB of test media and will report my results later.
Using VP11 with GPU on, SCS's test project rendered the MC AVC Internet template in 101 seconds.
This is 6.6% slower than their report of 94 seconds for the Radeon HD 6870 and 23.7% slower than their GTX 570.
I don't plan to push the 560Ti's overclocking beyond the factory overclocking done by it's manufacturer, Galaxy, although I read somewhere it can be pushed close to the 570.