Thank you both,

So I guess what you're saying is that we can exceed the max/upper voltage calculated by Geckos equations, so long as we don't increase the temperature sufficiently to cause demagnetisation or a fire.

My other take-away is that there must be a margin in Geckos equations, so rather than being an absolute max/upper voltage it's perhaps just an indicator, otherwise there'd be a lot more issues with 68V on these motors.

I'm away for the next couple of weeks but I'll increase the current to the motors when I'm back (to what it should be) and see how that increases the temperature over the runs I do and take it from there.