Those are about 2x faster than your 2014 iMac when editing 4k H264 due to the improved Kaby Lake version of Quick Sync. Your best bet for a hardware upgrade is get a pre-owned or Apple-refurbished 2017 iMac 27. The 2013 Mac Pro works pretty well on H264 1080p material or 4k ProRes but not on 4k H264. You can create proxies and edit in proxy mode, that's about it. It is a CPU bottleneck caused by software decoding of H264, vs Quick Sync hardware decoding. There is nothing you can do to upgrade the Mac Pro to fix this. That probably explains why your iMac feels more responsive. Since the Xeon-powered 2013 iMac Pro does not have Quick Sync this will be much more laggy than the same material on a 2014 iMac 27. You are probably editing 4k H264 or some variant of this such as Sony XAVC-S. #EDIT Sorry, I just realized that I posted this in the FCPX topic instead of Hardware. Will 64GB be really noticeable compared to say 48GB? If RAM upgrade is the way to go, I am torn between going for : Question 2: Considering that the MacPro is pretty old in computer years, I am hesitant to invest a huge amount in upgrading unless it'll feel like a Porsche again thanks to the upgrade, To clarify: I am not too bothered about render times - it's more the snappiness of the system whilst editing (and playback of unrendered segments). I am not very savvy in which hardware is responsible for which tasks, so my question is: will upgrading my RAM in the MacPro help speed things up or is it more a GPU issue? Working on a short 4K project with chroma key, the Mac Pro lags very noticeably when clicking through the timeline and needs to render to playback smoothly. Editing off an external SSD via USB C/3.0. I switch between the two machines when working from home/office. My iMac 5K (late 2014) has 24GB RAM, i7 4GHZ 4-core, 512GB SSD, AMD Radeon R9 M295X 4GB VRAM My MacPro (late 2013) has 16GB RAM, 3.5GHz 6-core, 512GB SSD, 2x AMD Fire Pro D500 3GB DDR5 VRAM

Updating memory on late 2013 imac