The ONE great thing about a 40x burner is that it can do 20x CLV.
All burners 16x and above burn for a while at a lower speed. Stop. Burn at a faster speed. Stop. Burn at the fastest speed for the last third of the cd and eject.
This, ladies and gentleman is a BAD THING. Why? Because CD's were never specced for having GAPS in the recording! Using the "burn-proof" algorithms, some areas on the CD are marked so they are skipped by the error correction mechanism on the reader, so you SEEM to get correct data out of them... but that's not guaranteed.
Why? Because there's only SO much the ECC on the reader can do. Every minute scratch, every dust particle, every time you lay a CD on top of another CD, it all causes microscopic damage that the error correction can deal with. But when a sector is already relying on being error-corrected to be read (burn-proofed sectors are!), any more damage to it will make it plain unreadable (i.e. - if you have two scratches that intersect on one spot of the CD, that spot is more likely to be dead than other spots with only a single scratch - because there's more that the ECC can see on the CD with only one scratch. Think of dragging a nail across the CD every time you see your burnproof kick in, or the recording process stops and restarts.
So, with a 40x burner, you can do a 20x burn without stops and starts. No damaged discs, and no disks with little concentric circles on them (I've seen disks made on these high-speed cheap CDR's, this is the exact pattern of damage that's most difficult for ECC to correct)..
Just a thought.
The only exception to the above are Yamaha burners that gradually spin the CD speed up as it goes through the burn - still don't reach max speed at the beginning, but at least they don't stop recording, so you get a quality burn.
FYI: My Plextor 8x burns an 80minute CDR in 11 minutes. Not bad for three year old technology, eh? It's SCSI, it has 4mb buffer (IMHO, due to the above, we should boycott all CDRW's with less than 512K buffer per 1X of recording speed), and NO burnproof. So I either get a perfect CDR, or an error - the drive doesn't lie to me about making a good CDR when it's using cludges to make it readable for a few months until the disk dies.