How much RPM are we currently getting? Will check that at the workshop tomorrow and provide the answer. From what I remember is that we are limited hard-coded by the firmware to F1000 and default in GC is F800. Wow that relates to RPM and how fast we could actually go is from my perspective somethig that people like (alphabetically) @bar @blurfl @dlang @MeticulousMaynard @Orob @zaneclaes and sorry for those i missed would be able to answer. The true ratio, the true Amps is something to be checked and tested thoroughly before designing a new shield (if that is even necessary).
Edit: @krkeegan is one of my misses, i apologize. Please feel free to add the others i missed.