paste is usually not going to give you more than 3c - 5c
a side panel fan might help more if it blows over the card
a aftermarket cooler would probably bring the biggest gains (like the accelero extreme), trouble is the really good ones are a bit more expensive than they need to be.
I can't find my hard numbers as I had an HDD go south, but I'm pretty sure I got 10C on my bottom card and 7C on my top one when in the most demanding areas of XIV (ie low res bushes!) and a slightly lower fanspeed and less noise because of it. I forget what paste I used first (I think it was AS5) but it only netted like 5C difference, MX2 did the trick. I'm running in a HAFX so my case has plenty of GPU cooling the 470s just didn't like the shrubbery in XIV. We'll see how well those results hold when I move to the muggy coast of North Carolina, the UK doesn't really get that warm the majority of the year. Also in my instance I couldn't use the aftermarket coolers, I could have one one card but not both and the card I couldn't do would be my top one which was the one requiring attention. One of these days I'll get smart and just go with water, but the upfront costs keep me upgrading my PC and playing with air instead.
Besides that the Crystal engine doesn't scale very well with SLI/Xfire setups either
Um 55ish %scaling increase here on near max settings for SLI that's roughly the same is what I get in Stalker CoP. There are titles that scale better, but there are more that scale much worse. Edited, Mar 30th 2012 3:20pm by Perrin
FFXI:Sylph - Perrin 75 Hume THF; Retired (At least from my use any way)
EVE Online:ScraperX; Retired
WAR:IronClaw- Peryn SW;SkullThrone- Grymloc BO; Retired