I have a pretty old gaming rig that has an old Gigabyte Z68A-D3H-B3 rev 1.0 MB with an i7 2600k cpu. It has 2 EVGA GTX 570s in SLI but wanted to upgrade the GPUs to a single, more powerful GPU without downright buying a whole new PC (since everything is in need of an upgrade). What would be the most powerful GPU i could purchase for the MB and CPU to still work with? (to avoid bottlenecking as much as possible) Thank you so much for the help!