Not unless you are running multiple monitors and need more Vram. VirtualLarry, just to drive the point home, you can see my rigs in my sig below. I use the 680GTX in rig 2 because of the 3 monitors. Rig 3 also has a 2g Vram 6970 but the 680 GTX is clearly faster for 3 monitors. Now, just for fun I hooked up the Hanns G HZ281 ( a 27.5 inch 1920 x 1080 monitor) to rig 2 ( disconnected the 3 24" monitors).
I went from the same cpu, ram and nearly same HDD with 2 5850 in CF to a 680 GTX. Guess what? Feels about the same. Those 6870s in CF will last you a long time. If I owned them with 1 1920 x 1080 monitor I would snag either a z68 MB and 2500k or the newer z77 with a 3570. OC the CPU and let those twin GPU puppies breathe. You have too much $$$ invested to jump to a 7970 or 680 for bragging rights. ONLY if you go multiple monitors where you need more Vram would I get a faster card.