There’s more than just the V Wheels vs linear rails at play (pun intended) here.
The drive belts, frame and extrusion deflections all contribute too. The machine deflection also varies substantially for the same stiffness as frequency increases as the mass tends to damp higher frequency vibration.
My measurements on an SO3 indicated that the major contributor was the V Wheels, now that I have linear rail on the X axis my deflections are much smaller but the machine still deflects and vibrates when cutting, just quite a lot less.
Cutting speed measurements are quite sensitive to cutter, stickout, workpiece material (this specific sample when we’re talking wood), feed rate, RPM etc. It’s a worthy goal, but somewhat more complex than one might hope.