Any time i work with this footage, i try to get it away from the original file as soon as possible. It becomes pretty heavy lifting, pretty quickly for the box. Trying to play down a timeline of any significant length can be a challenge trying to keep audio and video in sync.
If you are doing an online somewhere else, than a lower Dnx is fine, but your box can handle it at 180.
If you switch to FCP, i would suggest converting the original to prores 422 and working in that as well. Either format will work for your final online version, and won’t put too much strain on your box.
I usually use mpeg stream clip for my conversions in final cut pro. They go quite fast, and you can batch them using multiple processors for an added speed boost.
Either way, don’t work in H264.
Glenn