Mach4, being under development, may behave differently but...
Both the S### and F### commands will break the Constant Velocity chain so your Gcode example will not flow smoothly. Unfortunately this is a function of Mach3 and there is no direct solution. (an indirect solution for replacing the S### commands with a spare axis electronically or mechanically driving an encoder, or similar, has been used with laser systems but this may not suit your requirements).
Perhaps reconsider the way you wish to operate your machine ?
Tweakie.