I'm not confident that the usual .55 mach is all that helpful unless applied as a limiter to a well-developed existing port (where the basic design is not a variable).
The mean air speed (which is what this determines) isn't what's actually happening in the port except during a small proportion of the time. If there were no other inputs it would be useful, but there are more factors that are not considered.
An (easy) one is rod ratio: how much change in "leverage" does the descending piston have against the port. At TDC: none, at BDC: none. At maximum piston velocity (almost always between 71 and 78° ATDC): highest (lagging port and chamber volume somewhat). The rod ratio here (7.5625" ÷ 4.1875" = 1.806:1) is similar to other high-performance engines, and some comparisons will have value.
Another is static CR: very high means that the vacuum signal is not buffered by chamber volume, but acts more directly against port volume on valve opening. High CR works the port harder.
Obviously, the worst example is a badly-shaped large port, which will have very low velocity for its X-area, but also low CFM. A straight port (EFI, DOHC) with 2.5:1 "n" can be very small and work very well even above .55.
What I'm confused about is the effect of the high bowl volume in any siamese-port engine, where the charge mass "waiting" directly above the valve is very large compared to both port volume and port X-area.
