Mac Pro Encoder Performance Bottleneck

Both our iMac and Mac Pro are on Monterey running Premiere and Encoder 2023.

The iMac makes quick work of proxies, but the 2020 Mac Pro goes slow and hangs. Once it starts processing the system cpu usage in activity monitor goes way up while the user cpu% is lower which is the opposite on the iMac. The iMac has higher user cpu%, like 82%.

A 20+ minute interview took 7mins to proxy on the iMac pro and 40mins. on the MacPro.

What could be the reason for this difference and for Encoder showing up as a system process instead of a user process on the Mac Pro?