FCP runs out of application memory

I have a 40 minute project with a lot of archival clips that are a different frame rates than my project (cutting in 23.98, lot of the archival is 29.97 with some 25). I went through and changed the rate conform to optical flow, planning to let it run overnight analyzing and rendering. Unfortunately that has not gone to plan. FCPX eats up all the memory in about 45-60min and I have to force quit. Rebooting the system doesn't help. This is with only FCPX running, no other applications. Activity Monitor shows FCPX taking about 112gb of RAM before it finally craps out.

This is on a 2013 Mac Pro (trashcan) 6-Core with D700 gpu and 64gb of RAM.

Any suggestions would be appreciated.

And before you ask why I'm cutting in 23.98 when so much of the footage is not, it has a theatrical screening and distribution, those are the delivery specs (it's a feature, but the first 40min lives in it's own Library and Project). And optical flow works great for this, I'm just not able to set and let it do its thing.