Go for the 670 SLI, it will be cheaper and almost identical performance to the 690. Overclock them and you may surpass the 690.
670 SLI = $800
GTX 690 = $1000+
You really do not need to go with Ivy Bridge , its not a good upgrade from Sandy Bridge.
You would be better off overclocking that awesome i5 2500K of yours and enjoy the speed of it, or go with an i7 2600K and overclock the hell out of that!
Thats my opinion