Juraj is correct in his statement about the smoothed motions being splines, and therefore we cannot output them as circular motions for the machines.
As for your slow transfer motion problem, I am glad to say that we have a solution for this. The requirements driving this project made for the option to turn the smoothing on or off for the rapid motions. As one customer told us, some machines can't handle such smoothing on their transfers because they shake so badly they would rumble the building. Other machines don't have such problems. So to address this issue we have made smoothing transfer motions optional in an upcoming version with a toggle switch in the same group of the Smoothing tab. When you select the Smooth Corners toggle, another pops up with the rest of the parameters allowing you to smooth all engage and retract motions, but have the option to leave the transfers unsmoothed.
By the way, there may be some confusion as to which smoothing option you are refering to. Are you speaking of "Override with Smooth Connections" in operations like Contour Area and Variable Contour? Or are you speaking about "Smooth Corners" which has been added to many of the planar type operations such as Cavity Mill, Floor Wall and Planar Mill?
It is smooth because the G1 moves are being interpolated. Another option is to change the Rapid output mode from G0 to G1. Then all of the former G0 moves will be G1.