07-26-2015, 01:57 PM
I'm not sure where you saw the 390 has less cores than the 290, they both have 2560. In fact the R9 390 is literally the exact same card as the R9 290, it's just a rebrand, so that would not be an upgrade.
Sane options for an upgrade would be GTX 970, GTX 980, GTX 980Ti, or GTX Titan X.
Sane options for an upgrade would be GTX 970, GTX 980, GTX 980Ti, or GTX Titan X.