tomfreak, two good 460s are somewhat less than a single 670 (VRAM limits not
withstanding), while two 560s will be similar since they're just oc'd 460s and
most of them had slower clocks than the best 460s. Two 560Tis can be usefully
better, matching a 670, or even matching a 680 if oc'd, but again VRAM capacity
may be an issue, though for all these older cards there were 2GB versions
available (but often with slower clocks; I have two oc'd 2GB 460s @ 800MHz
which run quite well). My gaming PC still has two 900MHz 1GB 560TIs which are
quicker than a 670 at stock, quicker than a 680 oc'd, at least when the 1GB limit
is not an issue. They certainly cope with Crysis2 at high detail well enough.
However, comparing to these newer 600/700 cards, the only older cards that
do still perform well by comparison (by that I mean the potential gain from SLI)
are the 570/580, again assuming VRAM capacity is not a factor, though the
3GB 580 definitely shines here. Indeed, two 580s SLI are almost identical in
performance to a single 780 for 3DMark11, eg. see:
http://www.tweaktown.com/reviews/5516/nvidia-geforce-gtx-770-2gb-video-card-review/index4.html
Here are my 3DMark11 results for two 797MHz 1.5GB 580s:
http://www.3dmark.com/3dm11/6683648
http://www.3dmark.com/3dm11/6683683
If you want lots more 460/560 data, see my site:
http://www.sgidepot.co.uk/sgi.html#PC
Ian.
PS. I don't include the 470/480 because they run too hot for my liking
and thus I wouldn't use either in SLI.