I dug through code to find out how Throttle setting works.
http://github.com/smokku/uae4all/blo...wcpu.cpp#L1323
and it's a... throttle.

It increases emulated CPU speed with the following rate: 1 1 4/3 4/3 3/2 3/2 4
(I don't know where did the menu numbers 0 10 20... came from, though.)

P.S. Changing it will not make any difference for VSync-based apps. (Like most games, demos etc.) It does not matter if the CPU finished a task earlier - VSync is still 50 times per second (or 60).