Safe to mix 4/0 and 1/0?

[solarstuff]

Thanks for those calculations. I am learning so much it makes my head swim

I am going to spend a little of my discretionary solar budget to upgrade all cables to 4/0 before I ask for more help.

I believed many of the posters are right: my system's good enough but not to exacting spec, which is probably why it's not behaving the way I hope/expect

Becak after some cutting and crimping to report the results!

That is a good reason for increasing the voltage but that is not the current issue for the OP nor do I think it is something he wants to consider. He just wants to get the temperature of one or two of his wires down.