Long length & low pitch is like low gear, pulls vertical better, flies the plane slower at full throttle, provides more drag/braking at low throttle.

Short length & high pitch is like high gear, gives you higher top speed, but vertical performance will suffer, less drag/braking at low throttle.

The prop loading factor is Pitch x Length^4. If you find a prop that gives you optimal RPMs, then another prop with a similar load factor should give you similar RPMs. This means if a 10x7 gives you optimal RPMs, then an 11x5 (11x4.8 actually) should give you about the same RPMs.