Hmm, Vectric Aspire has a Time Estimator. It gives 16:04 for 600 ipm rapids, there's a "Scale Factor" variable underneath that, set to "2.0". So, looks like they're just getting 7:02 min based on linear feedrate and rapids, and the Scale Factor is an arbitrary multiplier, it doesn't have a way to guess machine acceleration.
OK I found the "toolpath accuracy" option, it's not in the Toolpaths tab which is weird. It was set to the default 0.0004". I changed to 0.004, the file size dropped to 1/4 and the simulation time in Mach3 dropped to 15:52. Interesting.