Joe - I have a 12 x 5 on my .46 and it turns it fine. I think an 11 x 4 is a little on the small side. It's less work than a 10 x 6 which I also think is too small.

For each inch you add in one you subtract in the other and have the same load. This is a rule of thumb and not an exact swap.

9 x 7 = 10 x 6 = 11 x 5 = 12 x 4

See? All those props would turn about the same on any given engine. So if a 10 x 6 is too small then so are the others. But... wehn you start getting farther away from the "base" prop the rule starts to dissolve. In other words, the reality is that a 12 x 4 would probably not be too small. Hope that makes sense.

BTW - those are just an example - none of those props may work for your application.