boston62, timerguy, I din't think you can directly compare rpm even if you have the same pump. After reading Mark's terrific posts in Hyraulics 101 I understand the gpm put out by your pump will vary considerably depending upon the head it's pumping against. To find out the gpm your pump puts out you first have to calibrate it, and the easiest way to calibrate is to run it at 3450 rpm and note the watts. You then compare this to data available from CEC or APSP for your specific model.
For example the CEC data for my pump at 3450 rpm is:
1990 watts, 43 gpm
2340 watts, 71 gpm
2720 watts, 97 gpm
So the lower the watts, the lower the flow, and the variance can be huge depending on the head loss in your system.
My pump draws 2866 watts at 3450 rpm so I figure its pumping about 106 gpm. If I understood Mark's posts correctly, the gpm at any other speed is directly proportional to rpm, so for me the gpm at 1500 rpm would be 106*1500/3450 = 46 gpm. but for you guys it could be way different depending upon your plumbing.
It's really interesting to run the pump at different speeds, note the watts and then calculate the watts/gpm for your pump and your system. My pump goes from 4.2 watts/gpm at 800 rpm, up to 27 watts/gpm at 3450.
I guess another advantage of VS pumps is they generate enough information to keep geeks interested and out of other mischief.