The new P-CAV drives do seem to produce more and more errors when te speed goed further up.
But now looking at Z-CLV we find some indications that speed isn't the point.
Now a lot of these zone writers have most errors in the first and last zones.(Based on the pictures of the Dutch Magazine Pc-Active)
And the first zone is the slowest speed. So it isn't about speed only.
This test also showed more proof that speed isn't the main point
Since the fastest drive in that test the Plexwriter 40/12/40A produced the lowest error rate. The other drives where 32x recorders of Philips, Freecom,Aopen, TDK. However one thing was noticed the Plextor drives was sometimes slower with burning as the 32x writers, but then again it was the only drive of the which produced decent disc's according to the test. Looks like powerrec II does it's job.
So speed isn't the only thing. It is about the optimised writing strategy of the burner for most media and the quality standards of the manufacturer.
And like John says there is a lot of difference between the writing qualtiy which is good enough according to the manufacturer.