I've been sporting 2x8800GTS in SLi for a while now, and whilst it runs almost every I want happily in 1920x1080, there are a few games I can't quite max out, and was thinking of getting an upgrade.
My trouble is I don't actually know what the comparison between these two cards in SLi and a single card in the 200/400 series is actually like. I'd probably keep one of my 8800s for physx, even though it seems a rarity in games.
How much attention should I pay to things like texture fill rate etc? I was contemplating a 470 and noticed it had a lower texture fill rate, what does that actually mean?
I think you will better with your current setup now, 2x 8800GTS on SLI is still strong enough to play any games recently...
Just with "few" games that you can't maxed out, it doesn't mean you have to upgrade.
I'd probably hold off if your current setup is still performing well. The HD5850 or GTX 470 will be a modest upgrade at stock and not really worth the money imo. They both OC a ton though, and especially the HD5850(cheaper, OCs more) may be worth it if you do so.
++1 to keep the current setup.
If you do decide to upgrade, stick with the Nvidia 470, it is possible to use PhysX with an ATI card as primary renderer but the workarounds rely on Nvidia not changing their older drivers to prevent this.
You might also consider a pair of GTX260s' for SLI if you are not too worried about DX11, the power consumption and noise- A few E-tailers are selling their old stock off now
Keep your set up.
Certainly don't upgrade to two GTX260s, for a start they aer overpriced, secondly they are old technology which you will have to replace again in a year.
When you do upgrade, unless Nvidia have come out with better GPUs than the 470/480 then go with a 5850 or 5870. The 470 is inferior to the 5870 yet costs disturbingly close. The 480 is a bit better than the 480 but costs way too much. The Nvidia cards are also too hot, too loud and too power hungry to justify buying them for a gaming system