i have a similar problem with Tyrian 2000. Speedset makes utterly no difference to the sound except that if i set it to -60, midi music stops working entirely.
It seems every game i run suffers from the music being about 2/3 of the speed it should be. i've messed with all the options, changed dma timings, turned everything off and on, and still the music is too slow.
Tyrian's setup program seems to eventually fix the problem in jukebox mode (when its showing a sort of Technicolor starfield and playing music), the speed wavers a little and then evens out to a constant rate, which is still slower than it should be.
I tried increasing the priority of the process in win2k's task manager but to no avail.
In other games (e.g. supaplex, which i tried because it's said to use unorthodox timing loops to detect audio hardware), speedset has made a difference, although much too much of one. at -3 the music is at least twice as fast as it should be, and at -2 it seemed no different to what it was like without speedset.
*in all cases* the first second or two of the music is played at *exactly* the right speed, then it gets sloooowweerrr. Maybe this is something to do with Windows automatically lowering the priority of a thread or process? thats what it looks like to an uneducated observer (me).
Athlon 1.4ghz, win2k (all service packs), sblive, ati radeon 8500, directx 8.1b