Maybe the yellow-tip wood MA's are a higher load:
http://masterairscrew.com/12x6woodseriespropeller.aspx
I will try some other 12x6's and see if I can get nearer 10,000.
The 11,240 I got with the with the Graupner 11x6 calculates to .96hp and 6.19lbs of static thrust. That actually sounds about right for a .52 4-stroke. I don't know why the wood 12x6 is bogging it down so much. Maybe it's a miss-marked 12x8?
David