it may depend on where you are running the caldera.
my friend had one that he put a tmaxx roll cage/body panels on. this added some weight. he had the stock gearing and ran a 2s lipo. In a sand pit he ran a full pack. when he put in a second pack tho, it only ran for a minute before it thermal shutdown due to heat. While he had stock gearing, the added weight combined with running in deep sand and up sand hills was to much for the motor.
If on flatter/harder ground, the increased gearing may be ok. I assumed based on my friends truck that gearing up might not be wise. But I havent done it myself. If Dads has run 15t without issue then it may be fine on the right surfaces.
I dont like to have my ESC's run over 140=150 degrees. Motors can run 160 and be safe. I have run a brushless motor as hot as 190 before without damage...but 160 is a better range for long life.
Temp guns are $15-$20...and worth the price if you want to experiment with gearing or different batterys or different tire sizes. Its alot cheaper than having to replace your ESC or motor because they got to hot. While the ESC has a thermal shutdown, you cant always rely on that stuff....and it doesnt kick in until the temps reach a dangerously high range.
My trusty duratrax temp gun has prevented me from burning up more than a few systems!