From my research it looks like it is possible to put the 2017 iMac 5k Logic Board in my Late 2015 iMac. It appears the only modification would Making new holes for the the TB3 connectors. The reason for wanting to do this is to have the improved graphics card and TB3 for EGPU use. I already ran a script so I could use an egpu on my machine and it was a downgrade.... the TB2 cables are just too slow to use an egpu for FCPX. Please advise, I do heavy video editing on FCPX 10.4.6.
Current machine:
iMac Late 2015 5K 27" Retina
OS: Mojave 10.14.4
Processor: 4GHz intel core i7
Memory: 32GB 1867 MHz DDR3
1 TB Internal HD SSD
Graphics: AMD Radeon R9 M395X 4 GB
Heavy editing of what kind of footage? 4K multi-cam? H.264? H.265? The iMac you are running on right now is quite a stout machine...are you transcoding your footage? Do you use proxies? Do you use external storage to store your Projects and Libraries? Are you using a 1TB SSD or a 1TB Fusion Drive? Your description says HD SSD, which is kind of confusing.
External SSD storage for working files can help immensely.
Apple doesn’t just hand out motherboards to anyone and everyone who asks. Chances are that is strictly sold as a replacement part and the cost starts at $999 and goes up from there. And you would have to prove you own a 2017 model with a faulty logic board to do an exchange.
If your are doing H.265 editing, you need to move up to a 2019 model with an SSD and even then it can be hard to digest.
Otherwise, check out LarryJordan.com and Max Yuryev on YouTube for some better insight into optimizing your FinalCut Pro X workflow. Good luck!
EDIT: Although the 2017 iMac uses the same Z170 PCH the 2015 model uses, I doubt very much if you can simply plop in the 6700K from your 2015 and have it just work. I suspect the firmware is locked to prevent it as well.
