rrob -- (1) Assume you have to start from scratch and install/restore everything as wuzy suggested, unless you're willing to do a bit of experimenting as sub mesa suggested.
(2) Yes, you are likely to get quite good performance with that setup, and the Adaptec is definitely a step up from the Intel ICHR. (I hope you bought the BBU for the Adaptec?) However, RAID-0's benefit is improved sustained xfer rate; if that isn't your performance bottleneck (and it rarely is), you're unlikely to see much of a real-world performance improvement.
(3) Assuming, based on your previous posts, that you're trying to get a performance improvement in a heavy VM environment, I think you're going to be a bit disappointed (RAID-0 is not the solution to that problem, unless you have very weird workloads). RAID-1, or better RAID-10 (assuming you can afford the loss of disk space), would likely be preferrable, especially with a decent controller such as the Adaptec and with BBU cache.
sub mesa -- Neat trick if it works, and easy enough to test. Assuming one of those RAID-0 arrays is what rrob is booting from, it'll either boot or it won't once he's created the array in the Adaptec BIOS. My guess is it won't, but I'd be happy to be proved wrong.
Have you seen it work or this theory? I ask because I'm very skeptical based on past experience (at least with LSI). Not to mention that it would require that the Intel and Adaptec metadata are compatible, and placed in compatible physical locations on the drives in the array so they don't step on anything else important, and that the resulting on-disk-structure was also block-for-block compatible. RAID-1? Maybe. RAID-0? Unlikely. Anything other RAID (except maybe RAID-4)? A snowball's chance.
OTOH, it's an interesting thought... would be cool if Intel and another vendor were to get together and make their metadata compatible so there was a nice and easy upgrade (or downgrade) path.