That engine will unload at least a 1000 rpm in the air and more in a dive plus it will pull best around 10,000 static. Anybody running these motors much over 10,000 will be sorry sooner or later. Blowing up expensive motors because of ignorance seems like a real waste.
I originally had a MA 11x7 on mine and tached it at 11,400 using Omega 15%. I have an APC 12x6 on it now which seems to be the best prop for the Sig Kavalier. I must have forgotten to note what I tached, but will get it next time I fly the plane. I really don't do much WOT stuff with it as the Kav is pretty fast except for uplines.
I've had the .56 for about 3 years and have close to 200 flights on it. I'm not propping mine out of ignorance. The props listed in the Saito manuals are suggested props for initial setups based on APC props and 15% fuel. The list is not a requirement or limitation. The 11,200 and 11,400 RPMs noted are a bit high. I wouldn't be afraid of this prop size, but I agree that the engine probably pulls better at lower RPMs.