I know I saw a big improvement when I went from 5400 RPM disks to 7200. I think you have your disk allocation bass-ackwards though. Use the faster disk for the data that will get accessed the most - your audio data. It also depends somewhat on how your software utilizes disk space and what sort of work you do.
Whether 10K is a big step up from 7200, I don't know (I ain't been there). As long as there aren't any other bottlenecks in the system, I would expect some improvement.
Also consider the addition noise a faster disk might make and additional heat.