My cpus are running at 90 C, is that too hot?
Depends on the CPU, if your CPU thinks it's running too hot, it should thermal throttle automaticaly. Just keep an eye on it and make sure it doesn't get any higher than 90.
You might want to check your cpu heatsink and cooling fan. Keeping them dust free help keep your cpu cooler.
Also, you can remove your heatsink, clean it, and apply a fresh coat of good thermal paste. That'll cool your hot cpu down a bit.