mj147,
If you're not a fan of "loud screaming engines", then you should really consider a 4 stroke engine. There are a number of manufacturers producing 4 strokes in the 52 size range which would work well for a 40 size plane.
A nice throaty growl instead of that mosquito "whine" of a 2 stroke. Quieter too.
The one problem I can see, once you fly a 4 stroke, you might not be happy with 2's again.
Dennis-