I have Radeon 6990, should I upgrade to R290X or just wait for next gen?

Gaidax

Distinguished
So here is the deal, I already have Radeon 6990, which is pretty powerful. A single R290X is about 30% more powerful on average in about 10 tested titles.

I have an option to toss a bit of money and get R290X while e-baying my 6990 (miners grab it like hot cakes for 200-250$ it seems).

The question is, when will the next gen AMD/Nvidia card will pop out and if it is not smart to simply wait a couple of months to get that instead, seeing that 30% extra performance is snazzy, but it's not THAT huge really, although it's definitely not 0 and you won't have to pray for Crossfire to work either.

What would you do?