Ok, just reverted to current release and re-applied beta patch, much better; graphical issues appear to be gone and a significant FPS increase - pre-patch Black Death was Avg 47 - Max 127 - Min 2, post patch was Avg 53 - Max 126 - Min 15.
I'm not convinced that I haven't now got some microstutter but without reverting again to check I don't know if it's just me looking harder
