Surely I should be able to edit this footage..?

10-bit HEVC is super hard to process in real-time. It stutters in QT too I’d think. Either optimize or work with proxy. For 4K I’d go with proxies. Easy to create, light weight, system processes and plays back multiple tracks.

What’s the codec? The drive isn’t the problem, the codec and the bit depth might be. You might need to work with proxy media, especially for the multicam. 10-bit is difficult to process in real-time. An M1 Mac can only run three channels of 10-bit multicam.

Though in theory your RAID should be able to handle it, it may be worth testing with the same media served from the built-in drive. If you can’t work smoothly with that media when coming from the built-in drive you you will need to work with proxies.

It is a good thing that FCP has a “proxies preffered” option; you need only make proxies for the files that need them.

Because of the nature of my work, I have a ton of footage. I'm trying to upgrade a lot of training videos we've made.

Converting all my Multicam clips to Proxy will use masses more HD space (insert appropriate sad emoji here).

I'm not familiar with the "proxies preferred" option, Luis, and I couldn't find any reference to it in Prefs - please explain??

This is selected from the little View menu at the top right of the Viewer:

It used to be that you had only two choices: "Optimized/Original" and "Proxy".

So even if only a few clips needed to have proxies for smooth playback, you'd have to create proxies for everything.

Now (since 10.5?), you have a third option "Proxy Preferred", as seen above.

What this means is that a proxy will be used if available, and otherwise FCP will use the optimized or original.

Suppose you have one of these "difficult" clips in a project and a bunch of 720p clips. In the old days, you'd have to make proxies for everything. Now you could make a proxy for just that clip.

Another thought that just occurred to me: did you try leaving the playback at Optimized/Original but select "Better Performance"?