Different drives like different discs. FWIW I get results very similar to cfitz's TY results using my Teac 24x at 24x on Mitsui 16x SG media. I haven't tried any faster as I use these media at 4x on a Yamaha drive using the Audio mastering doobry for best results on audio discs I want to keep (copying originals in this way actually makes the copies sound slightly better than the originals on my hifi!).
Basically, as long as the C1 error count averages less than 30 with no C2 errors I don't see any real problem.