NTSC mode isn't any faster. It may appear so when software is timed by vertical blanking only. Running NTSC screens in PAL mode (with a blank bar at the bottom) may speed things up a bit since there's less bitmap DMA going on, increasing Blitter time and CPU time for DMA intense graphic modes.
(Yes, a real NTSC machine really is a tiny bit faster (7.16 vs 7.09 MHz CPU clock), but this isn't noticable and can't be changed by switching to NTSC video timing.)
As to "switches on NTSC but gives full PAL height resolution" I don't understand what you mean. The difference in NTSC and PAL (amiga-wise) is the number of horizontal lines thus screen height.
