Today NVIDIA releases their new GeForce GTX 590 flagship which is based on two GTX 580 GPUs working on a single card. AMD released their dual-GPU HD 6990 design just two weeks ago, with power and heat being the decisive limit on performance it will be a tough fight between those cards.
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips