There are discs and tracks that the 40x will positively not handle - or can only handle when the DAE speed has been throttled down to 4x. I know because I have one. Perhaps the 16x doesn't have a problem with those items and can still do a multi-speed extraction.

That said, I wouldn't trade this drive for another. When you get a proper disc, it's amazing to see the speed go from 18x up to 40x - and the rip (complete disc) is done in 2 to 3 minutes.

Bruno