I have a V9 PS2 and my friend has a v7 and even when I hit my datasafe ricohjpnr01s at 8x, neither of the ps2s even bat an eyelid. In all my hours of watching movies on my ps2, I've only ever seen 2 glitches (2 separate instances) and they were down to not so wonderful media. But still, averaging PIs of 1000+ in kprobe and I only had ONE glitch. not even freeze, but a skip, so the ps2 is really good with half decent media. I don't even hear my laser moving around as much as when I watch an original dvd. datasafe, arita and verbatim are highly recommended for any burner.
PS - reminds me of when I used to hear not to burn audio faster than 8x, and not to burn ps1 discs faster than about 4x because that'd increase loading times. good discs are the answer.