First – are you using internal storage (the system drive) for your media? That’s not a good plan. It is a bad plan. So how are you accessing your 4K media? Or any of your media?
Second, what are your deliverables? If you are going to be delivering in HD, you could simply transcode to HD and edit on a 1080 timeline. Perhaps replace select shots with the 4K originals if you want to tweak framing and such.
If you are supposed to finish with a 4K master, then you are looking at a proxy workflow, and perhaps might be needing to plan for better media storage solutions, if that is a current issue.
System:
Dell Precision T7600 (x2)
Win 7 64-bit
32GB RAM
Adobe CC 2015.02 (as of 6/2016)
256GB SSD system drive
4 internal media drives RAID 5
Typically cutting short form from HD MP4 and P2 MXF.