I usually burn audio cds at 8x or 16x depending of the dirve.
I have done several tests to see which is the best burning speeds for my drives:
4x ----> Bad results (high c1 and jitter)
8x ----> Best results (low c1 and jitter)
16x —> Good results (a bit higher than burning at 8x, but it’s OK)
24x and up —> Unacceptable (not readable, c2, etc)
4x —> Average results (medium c1 and jitter)
10x —> Good results
16x —> Best results
24x and up —> Haven’t tested
You have to test your drives, but usually 8x or 16x for me are the best burning speeds.