Thought id create this post for anyone interested.
I was looking to upgrade the HDD's in my R4, so went for 4 x Seagate EXOS Enterprise 8TB drives. Found them for a great price.
About a week ago I set them up in RAID 5. It took about 24 hours for the disks to synchronise, and I now have 24tb of useable storage space.
My blackmagic disk speed checker gave me between 700-800 write, and around 600-700 read, and I'm delighted to find that it has worked flawlessly in Resolve and Final cut with 4k Prores 422 content. (I've been editing alot over the past week)
Im currently running an M1 Max Macbook Pro via an Apple Thunderbolt 2 to 3 adapter cable too. (I know some people have been concerned about compatibility with Apple Silicon. Updating to the latest firmware and drivers has done the trick)
If i encouter any problems I will be sure to post about it here.