I'd recommend against this unless you're seasoned enough to be able to fix issues from the command line, hold back disagreeable drivers via apt, and generally maintain your box without logging into X. Not that those skills will be required, but rather that that general level of competence with system maintenance should be there before you begin to purposefully mismatch system parts.
I'm running the 2.6.27-rt kernel in 8.10 and find it to work fine - there are a few more xruns than in 8.04, but I've been working around that. I only have one core to my processor so the shutdown issue is the only bug I run into.
I would personally expect more issues running a 2.6.24-rt kernel in 8.10 than a 2.6.27-rt kernel. Though I'm no kernel expert - have never even built my own.