RE: Bigger prop for break in?
The 11x5 will be fine...
Edit:
The 11x5 will actually be better IMO than a 10x7 in that the 10x7 is a bit much for a .40 especially a new one...and the 11x5 will have more flywheel effect, so it should help with the idle quality.
FWIW, a10x6 or 10x5 or 9x6 would be better "break-in" props for a 2 stroke .40