Radiator is out, what can I do in the meantime?

Definitely not a bad idea to flush it out and take a peek at the thermostat.

I once had an issue with the heater not being very warm and the engine temperature would surge (from 180 to 210 back to 180 about every 15 seconds). I back-flushed the heater core and got a ton of gunk. Then hooked up a couple hoses and held them pointed skyward while I filled the core with a radiator cleaner. Back flushed it and got a ton more gunk out. The heater never worked so well before!

Short story long, since you've got the system empty, it's probably best to flush and inspect while you can.