Monitoring vacuum at cruise speed is far better that doing it at idle, but it's still a poor substitute for using a delay flash timing light and getting actual measurements of initial, centrifugal, and vacuum advance. I've been using strobe flash timing lights for over 50 years, so it's not like that's some new, untested kind of technology. Shade tree methods are for people who don't know how to do it right, or maybe they just don't care.
On numerous dyno tests I've documented, one degree too much timing advance robs as much power as being 5 degrees retarded from the optimum advance setting. That's not guesswork; it's a fact proved by measuring torque and RPM, and calculating horsepower from those measurements, with corrections for temperature and humidity. Making a wild guess on timing has no place in that kind of calculation.
Jerry
