You might be able to get away with squeezing a bit more speed out of your media (say 12x burnt at 16) but your jump sounds a bit excessive.
Beware of long term reliability issues and cross platform problems. You may find the discs become difficult to read later in life (I had a few Traxdata's age beyond reading after just 2 years and they were burnt within their stated range so beware). You may also find that a disc lent to someone else we will be unreadable on their hardware.
In fact, Heaven help you if you ever change YOUR hardware for the same reason...
Also beware of the rogue CD in the batch which has a thicker layer of dye on it and doesn't burn properly... at the rated burn speed you would probably get away with it, but at extreme velocities any defects in a disc are more likely to show.
Sure, I've been able to speed discs up a notch in the past, but I always verify them afterwards and do not trust them with anything important.
Have fun experimenting, but be careful if your data is irreplaceable.
Regards,
Garry.