I've been running a 10.5 here at my local track for a few months and settled on a 23/78. Some of the guys I run with (with B4's) run 24/81. Obviously that's over here in the states, so maybe you should start at like a 24/78 or a 25/81?
I guess the bottom line is don't be afraid to gear up - the motors don't seem to mind it. Just keep an eye on temps while you're playing with gearing, and go from there.
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