That is a great question. The funny thing is that I have flown the plane for about 8 months now and I still don't know the correct answer yet. I love to fly slow of the verge of stalling the wing a lot. I love harrier manuevers, high alphas, high alpha knife edges, hovering etc. I am also a big fan things like flat spins, inverted flat spins, knife edge loops, etc. So, my needs are very much not for speed, but I want response and vertical. I tried the 16x6 and it was faster, but I was not happen with its spin up when needed to correct in a hover. The 17x4W spun up very fast but the rpms weren't what I wanted. The 16.5x5W was what I ended up choosing. Honestly I thought about trying a 16x4W as well, but I am not sure my hobby shop has one. I heard that prop may go supersonic though, so I don't know I want that much noise. Has anyone here tried the 16x4W or a Zinger 16x5?