That's interesting, thanks for reporting.
The main change in the 2017-12-10 release is that I increased the physics accuracy. That will put a bit more load on the CPU, but I don't think it will be noticeable actually, at least not on powerful processors such as the i7. Maybe that is still the cause though. I guess the best workaround I can suggest at the moment is to lower the graphics quality a notch or two and see if that makes it run smooth.
And thanks, glad to hear you like the sim!