With the Castle Ice50, is it better to run at approx 80% or approx 70%?
In other words, if you have a choice of running higher up in the percentages than lower, which way generates less heat in the ESC?

I'm running at about 74% at the moment, but I have a prop to try that will be about 70% on the ESC.
Another prop to try means I'll be 80% or a bit over and in our heat in Australia, I would like to run as cool as possible.

Russell,
I don't think it makes much difference in the real world.  I say go fly and have fun.

If you are at 100% throttle then there are no heat spikes for switchin - unfortunately there is no governing either!  I like to shoot for 70% to 75% throttle to maximize the headroom for governing - but that is also about the worst place you can be for heat spikes due to switching.

Can't put my finger on it, but I believe Castle discourages high PWM because the ESC can go hotter, however low PWM settings makes the motor run hotter.

I agree with Crist - choose your best settings for flight performance, then do all you can to promote ESC cooling.