under or over geared?

[VintageMA]

Short of plain old experience, is there any way to calculate what will be the right gearing for a certain setup?

For example - current project CRT.5 - 3S Lipo with a MM and Hacker B50 8L. Motor KV is 3019, so I figured gearing it for around 30 - 35 mph would be good without requiring too much amp draw. Based on the hardened pinions Mike had in stock for the 5mm shaft I got a 13T and a 17T. The motor got pretty hot with the 13T, so I switched to the 17T (gearing for about 45mph) thinking that would probably be way overgeared - but eveything ran nice and warm. No temp gun with me during the run, but using my finger I could tell all temps were under ~120.