gaddster wrote: Would editing off an external SSD (Samsung 860 eve or similar) speed up my workflow)?
Currently I edit on a late 2012 iMac I7 24gb ram connected to a 6tb Raid drive and I also use an early 2018 MacBook Pro i7 linked to a lace Rugged 2tb usb-c?
This depends on several things: RAID config of your current Lacie 2big (RAID-0 or RAID-1), what part of your workflow is slow, your timeline characteristics and what codec you're using.
If you are editing H264 or proxies, the I/O load is quite limited. Your 2012 iMac is fairly old so it's more likely you're facing a CPU or GPU limitation not I/O.
However there are a few cases where FCPX is doing lots of small random I/Os totally separate from the large sequential I/Os for media. E.g, after importing new content when thumbnail and waveform generation are happening. An SSD might be faster for that phase vs a single drive (and a two-drive RAID-1 array has the performance of a single drive).
I have several 32TB 4-drive OWC Thunderbolt arrays with 4 7200 rpm drives in RAID-0, and have often compared them to my 8TB 4-drive OWC Thunderbay Mini with 4 SSDs in RAID-0. The SSD array benchmarks faster and is quieter but in practical terms it's usually not that much faster.
I was editing in pro res but started using proxy. Editing on the timeline was slow so I turned off background rendering too. When I add effects or cinema grade it was slowing down and footage would play back jumpy. Exporting can take a while too (only ever export to 1080, but edit 4k on a 1080 timeline
If it's slow using ProRes proxy and when adding effects, that is unlikely an I/O bottleneck if the media is on a two-drive RAID-0 array.
The I/O rate for a single stream of 1080p ProRes 422 (IOW proxy of 4k) will only be about 7 MB/sec, which is even less than 4k H264. It's just not very high. 4k ProRes 422 is pretty high so you can hit an I/O bottleneck sooner, but your two-drive RAID-0 array should handle a single stream of that no problem.
Using proxies and a 1080p timeline helps other aspects of editing performance, but that only goes so far.
Unfortunately I think your issue is a CPU or GPU limitation.
A pre-owned or refurbished 2017 iMac 27 with Radeon Pro 580 and SSD boot drive would be much faster than your 2012, and it's much cheaper than an iMac Pro. For H264 it's smoother than an iMac Pro since Quick Sync is faster than AMD's UVD/VCE transcoding logic. However if you edit ProRes this doesn't matter. For either one you'd need several Apple Thunderbolt 3-to-2 converters.
An external GPU won't help on a 2012 iMac since you really need Thunderbolt 3 to fully exploit that.
We are probably pretty close to the release of a new iMac so you could wait and evaluate that.