I called him about the exact same thing. He said he just advanced the timing it a little while using an a/f meter to keep it percise. He hadnt dyno'd so there arnt exact numbers to compare the 2, but i dont think its a big gain from 91 to 93. I ended up going with the 93 since they sell 87, 89 or 93 here.
overall i love the chip, felt ~10% gain in the butt dyno.