Have already emailed the report.zip (65MB!) to the provided support alias.
Thought I would repeat it here in case anyone else has the issues.
Since the 1.0.63 patch today, the game can suddenly drop from the comfortable 30-60 fps down to one every 2-3 seconds. There doesnt seem to be a fixed cause, I could be shopping or fighting (or thieving) and from that point on that save game is broken. Loading old saves immediately restores performance, loading the broken save goes back to sub 1fps uselessness.
Given the size, had to make it a Google Drive attachment.