How consistently can you drive? If you are good enough you can make gearing and timing adjustments, and see if your lap times change. Not much more scientific and measurable than that, and ultimately the point of making an adjustment. Motor temps are a function of the load you put on them (gearing and timing) and the ambient temperature. If it is hot where you are you can bet the motor will run a little warmer. You don't want to overheat a motor, so you have to have timing and gearing right. The size of your track dictates gearing, and timing will need to be within about a 4° window to have the motor in the sweet spot. If your motor isn't slow or hot, data logging info probably won't help make you any faster. Make a small change and see how it feels.

First question you need to answer is how good of a driver are you? If you crash a bunch and your lap times are all over the place, a slight change in gearing or timing isn't going to matter because you leave a bunch of time on the track. At that point it is better to concentrate your efforts on improving your driving.