How important is RPM in a blender?
I've used both a Vitamix 500 (not extensively) and a Thermomix TM31. I didn't know there was a difference in RPM, but I didn't notice too much difference in end-effect when both were turned up to full power. So I think it doesn't make much difference at those speeds anymore.

If you're having trouble milling spices though, it helps to heat them a while in the oven, to get rid of humidity and therefore make them more brittle.