I'm concerned about there being a big performance hit by running PhysX on a single card, though (despite having a 480). If I had SLI like you, it wouldn't be a big deal.
I also would think that the release 256 drivers, as well as an updated PhysX runtime might address this issue.
Looks like NVIDIA is aware of this, and a driver update will arrive next week. Link
. I'll probably keep my 9800 GT, as it doesn't require any external power and doesn't generate much heat. I've got my X-Fi right under the 480 so that card's cooling isn't affected.