Mokis will overheat and detonate w/ anything over 5% nitro - specially in summer temperatures (ask me how I know )
And 7500 rpm is about the right range for the 2.1, so I don't think that 22X8 is too big a prop. Mine spins an APC 20X10 happily at 7400 rpm with no overheating probs PROVIDED I keep the nitro to 5% or less.