You are correct Joe heavier wt oils are meant to be used in warmer climates and I do understand how oils work the wt used is based off the temperature range and once a heavier oil heats up it does become thinner and most oils have anti foaming agents in them and for most of the U.S. 10wt is fine for the majority of the equipment. Yes lighter oils heat up faster but they also cool off quicker if I am wrong explain to me how denser materials cool faster than less dense materials.
The models guys are building don't have proper cooling for the systems Freddy added a cooling fan and heat sink to his equipment. If you have proper cooling alowing you to run lighter oil your system will have less stress and last a lot longer and your battery life will be extended as well.
Here is a CAT fluid recommendation chart.
Travis