You will find that 16x8 prop will cause the plane to slow down in vertical ascend. Following are my results w/ different props:

APC 17x6@10,000: unlimited vertical, great acceleration, but is a little too high rev for my OS 1.60 FX

APC 17x8@9300: good speed, flies like a pattern plane. But slows down on vertical

APC 18x6W@9000: can hover and pull out, but is too heavy of a prop and cause the engine to respond sluggishly.

I will get myself a carbon fiber 18x6 one of these days, after I hone the landings.