i was burning my audio at 40x with my taiyo yuden fujifilms. These are the ones rated at 24x but burn with low error rates at 40x. If i wasn't so lazy, i would post the ATIP.
Anyway, i found some new 40x media, did some testing for errors and found that burning at 52x with my liteon, results in low error rates. So i now burn audio at 52 and the discs play in all my drives and my portable cd player just fine.
There is no one specific answer to give. You should perform your own test to see what works best for you.
The error rates which i refer to are the C1 errors, which are normal and are corrected by the player.