Just a follow-up. I have contacted support last week for the grinding issue and circular problem. They contacted me this morning to test the 1.0.8b1.
On my test, the beta 1 fix the problem for linear cornering and linear circle toolpath. I was able to run fast toolpath with or without circular interpolation enabled.
Info provided > All cornering will run a little slower, because a code change in 1.0.8b1 causes the motion planner to actually enforce acceleration and jerk limits. You lose a little speed, but the machine is actually following the correct path, and not overloading what the steppers (torque) are capable of.