Steve, I am not sure. But I would try the ABC MW3 prop. I have a 50" apache with a modified Zen and this thing is well past you're expectations. I also tried a 6717 (3) blade with lots of success.. I can't tell you exactly how fast because I just got my GPS and I have not had a chance to try it out. However this weekend I will be doing some testing and I can gladly post my results. I tryed the 275 and did not like it. Later[>:]