I've been testing a bunch on mine, and my analogy is like with a car. I felt like the 15*4 was like a car spinning it's tires coming out of the hole, it felt like it was wasting some of it's power over revving that prop. The 16*4w was more like the car bogging out of the hole. But once it spun up, there was a lot of bite with that prop, it just doesn't transition quite fast enough. The 14*6 was actually pretty good, much to my suprise. They've all been pretty good, I'm just looking for the best of the bunch, the 15*6 is next. I really liked it on my friend's UCD.