I have unlimited calling for state side calls so I discovered a long time ago the phone is your friend. I don't deal with anyone that hasn't a phone number listed and I have been know to phone them just to make sure there is someone there to pick it up. I have discovered a lot of places have people answering the phone and English is not there first language, sometimes they think they are speaking English and they speak it better then anyone else in the store/office, if I can't understand them then I don't order from them. Other places just don't bother answering, another place I bypass.Just by ground testing with a tach you will know if the prop is going to keep the engine in it's RPM range. Then flight testing will tell you if you are going to like the way it fly's your plane. I have a big box of props and spend a complete day sometimes looking for the prop that works for me. Someone else may not like the way my plane fly's with that prop, who cares, it's my plane. On that pattern plane I tested a lot of props but even with longer gear legs a 15 inch was as big as I could use, I did try a Graupner 14X7 three blade, it flew the plane but lacked any vertical pull, the plane just does everything better with the APC two blade. The engine is a YS 1.20 FZ, it is under it's Max. RPM range and works very well. If I went to bigger tires I could go up in size a little. I fly off of a flat dry lake bed or asphalt field. The LB is flat but not smooth. Once in a while I hit a clump of dirt with the prop but so far so good.