The 280x and 7970 have the same GPU chip. The 280x has some minor clock tweaks but they are basically the same card. You would see a very slim difference in FPS.
Another viable option would be possibly a GTX 760.
The 290x is rumored to be around $550 and honestly wouldn't be too much of an improvement to warrant the huge price jump. It is a brand new chip though, and not based on existing hardware.
Yes, I did write the "R9 290 (NOT 290X)" in my post, the one that comes out at the end of the month, not tomorrow
I was also wondering about the difference between the Asus Matrix 7970 Ghz Edition vs other 7970 Ghz Editions (and the R9 280X), seems asus raise the memory clock on the Matrix version but is it worth the $25 price jump compared to other 7970 Ghz Editions.