5mm minimum is my thought. How close is your heal to the chain stays?
so as an update, i re-measured my shell and as it turns out, MFG spec'd it wrong and it's actually 68mm. spindle and cranks fit fine, but the crank hits the non driveside chainstay!
i will try shimming it out on the NDS stay, but i also have the 134.5 spindle on hand if it comes to that.
how much clearance should i try to have between the crank arm and the chain stay to be safe? (flex etc)