Depends on the performance, I'd guess around a GTX 780.
The 290X is slightly faster than the Titan, the difference between the 290 and 290X is the same as the difference between the 7950 and 7970, so about ~ %7, which would put it between the 780 and Titan, apparently AMD are also coming up with new Drivers thats going to push the performance up, perhaps 5 to 10%, and very soon. possibly tomorrow.