[Darryl Ramm]

The iMac is a fairly thermally constrained design, they will throttle if pushed enough. The is a wide gap there between thermall handling in a iMac and real high-end system.

One great way to have a scorching 17" MBP is to have them full of dust, I opened mine up every 1-2 years and sucked lots of dust out of them... and replaced two fans on separate occasions, but sure the'll get hot anyhow. My 2016 MBP was much more efficient/less burnt lap for more performance.

May be time to ditch your old Firewire disk technology. Super fast PCIe/NVMe or Thunderbolt 3/NVMe SSDs are widely used now. Even a tiny little external USB 3.1 SATA SSD like a Samsung T5 will blow away your old FireWire drives.

You will not miss having to old SATA drives (even if SSD, that's slow SSD).. The first piece of advice on any new Mac with PCIe SSDs is to maximize the drive space there as much as you can to fit your sessions and possibly all your sample as well. Old advice about not running stuff on the systems drive does not apply with that super fast PCIe/NVMe technology. If you can ditch all those external drives it helps with reliability and just less hassle.