Blitz really is significantly more powerful than AMOS for moving graphics around. A factor of 2 or more isnt unrealistic, not to mention proper aga support, use of aga fetch modes, aga sprites, and so on. I did a rough test a while back and was able to move 11 (double buffered screen) 16x16 bobs with amos without dropping a frame. Using exact same bobs with blitz I stopped trying once I hit 30 'cos that was excessive for what I wanted to do already.
For games on the amiga its second only to ASM (although you can also use nline asm directly in Blitz (and with colons to seperate commands
I actually enjoy AMOSPro though. Its good fun, and fun to see what can be squeezed from it, but it just doesnt compare for raw speed/fluidity/flexibility, or in any way I can think of (apart from ease of use). That said AMOS is still capable of some decent stuff if you avoid it's weaknesses.