Partitioning Late 2012 iMac Pro

I am running a late 2012 iMac with OS 10.8.5 and Premiere Pro CC 2014. I am running this older software because I am in the midst of a feature film edit. My system has 1.1 terabytes and 32GB installed RAM. I do not want to upgrade my system in the middle of this complex edit, but would like to partition my computer so that I may have a newer version of Mac OS, DaVinci and Premiere running. My proposed workflow is to pull off all files not critical to this edit, run a Time Machine backup and then wipe/partition my HD. Then re-load the time machine BU onto 350-450gb and allocate the rest of the space to the new partition.

Are there any concerns with this workflow? Will partitioning my drive as described above slow down my old project in any known way?

Thanks!

Rob