Yes, I've since discovered this for myself. I mostly play Diablo3, and for that I never hit above 50°c. However, when running GTAV with everything turned to max, I hit 76°c in about 4 minutes flat.
I only paid €246 for the GPU though, and consider the performance boost I've gotten, and my now empty (and likely to stay that way) wallet, I'll not be returning the card any time soon. I had considered selling off my Nepton, going back to stock cooling, and trying to piece together a water cooling loop from a Raijintek Triton and a second hand WC block. for the GPU.
How likely that is I do not know, but I'll have to see what I can manage.
EDIT: I should also say that the GPU is new and unused.
Hmm, having looked at water block prices for the R9 290X, it's going to be a very long time before I have that sort of cash spare.
Would this be OK to use?
http://www.ebay.de/itm/Alphacool-Ne...plate-black-/121764685695?hash=item1c59bda77f It's going really cheap, and if it stays that low I may be able to afford the rest.