I should have thought about this before I started looking at Crossfire setups. While my board does support CrossFire, it seems like it'd be a waste to try it since the second PCI-E slot is only 4x. Back in January when I put this system together I never really planned on serious Eyefinity gaming where I'd need 2 GPUs...
So, if I want to keep the board and upgrade to a better card it'd have to be the 6990. Otherwise it doesn't really make much sense to step from a single 5870 to a single 6970 on an eyefinity setup IMO.
Best option I guess would be to tough it out with 5760x1080 at medium settings (or drop down to 1920x1080 on High/Ultra) and wait for some new tech to roll out and/or pricing to come down and do a fresh build.
*sigh*