I have had a bunch of ST90s. The best sport props are a 14x6 and a 13x8. The best 3D prop is a 15x4W. I tried a 14x4W on one. It was a heavy model but the prop was terrible. The 14x6 and 15x4W both out pulled it. I hovered the plane with all three. The 14x6 took 90% throttle the 15x4W took 75% throttle and the 14x4W would not hold the hover for very long at 100%. Maybe a lighter plane would be different but you still gotta figure the other two props are better.

David