Ever tried disabling 2 cores in the BIOS, and cranking the clock speeds on your 1090 a bit more higher?
By making it a quad core, your probably will be able to achieve atleast 10% higher clocks
I wouldn't recommend upgrading at this time, the minor increase in FPS u'll get won't justify the cost incurred. You should happily be able to keep the same chip atleast till the Haswell/SteamRoller generation comes by