IMO By the time you buy and install an aftermarket cooler and also get good VRM cooling, you might as well just spend a bit more and buy a used Tri-X version instead of a reference 290, since they will probably end up costing about the same.....and the Tri-x will hold its resell value a bit more than a modded reference card IMO.
I was looking at reference 290x's (30 more than a 290) Did the same calculations. By the time I got the the extra cooling I'd be pushing up near the custom cooling solutions that had a 90 day warranty. Warranty won out.