I'm not aware of any manufacturers that does not have blower performance charts for their VS blower equipped furnaces, either in the literature that comes with the unit, or available by other means.
You should take some time to look over the blower performance charts many manufacturers supply with their VS blower equipped units.
The charts are a little different than for standard blowers, because they have to give static pressure/CFM values for each of the motors airflow settings, so you have to be careful you are working off the correct part of the chart.
Here is an example of the Service Facts for an American Standard furnace, blower performance charts start on page 12.
http://markbeiser.com/HVAC/documents...2-9V-SF-1C.pdf