Anyway I resolved it. Nvidia to the rescue. I was already on 365.19 drivers so all I did was use GE to optimise the gfx settings and then no crashes.
Make of that what you will !
At least now half a day later I can have some explosive fun!
Apparently having a gamepad plugged in causes stutters? I tried steam offline and unplugging my controller and it's smooth as butter now. So not sure which it is..
Just using an assault chopper to destroy the earth moving bases, after a 4th try.
As predicted it was your PC settings & not the game