Same here, exactly the same symptoms and error message. None of the classic fixes work. This includes:
Jun 30 2018
May 10 2016
In 0.57 Stable this has increased dramatically for me & the 4 in my group. FPS has effectively doubled with this patch including looking into cities. Well done Devs, it is now playable all the time and doesn't reduce to unplayable levels in cities. Keep up the good work!
@moeb1us Dean Hall himself said over a year ago in this thread above that it would be fixed in a matter of months. It has now been over a year. I think its a little bit past 'Hang Tight'!