@freqmax
So does this mean I can remove the obviously wrong quote from alexh? (about system running at different speed when you toggle between PAL/NTSC display modes.. Amiga bus clock does NOT change, nor the CPU clock)
Some music players run at different speed because they're timed to the vertical blanking frequency, and not CIA timers (vertical blank rate is 50Hz for PAL and 60Hz for NTSC, CIA timer speed remains the same regardless of the display mode. PAL and NTSC systems do have different system base clocks and thus different CIA clocks. The system base clock - and thus the CIA base clock - do not change depending on the screenmode). The only speed gain in 3D games from NTSC is the smaller area to render.
*edit*
Now that I think about it, what MiniMig probably wants is the full deal: Changing the base clock aswell (that is really change between PAL and NTSC, not just the display mode). However, this cannot be done runtime (restart is needed).