I've been running SLI on an Intel platform since February (hadn't used Nvidia cards for 10 years prior). BFBC2 has been great. It's run fine under each driver release. The GPU utilization on both 580s has been near 100% at times while playing.
So I'm thinking there could be an issue with SLI and its interaction with that particular board?
If you haven't already, try updating your BIOS to the latest release. This has improved the situation for some people.
Also, just about every benchmark test uses the Intel platform (SLI or otherwise). If you are considering an upgrade, you may consider going that route.