My only question about your methodology is whether you're starting the segment from a dead stop and/or ending it with a stop. If so, your average speed may overly weight each bike's acceleration/deceleration profile (unless your riding style is to stop every 1.5 or so). Your method will tend to favor a bike that accelerates/decelerates quickly.

It really depends on your typical ride. When I commute, I stop and start every half mile or so. When I do a road ride, I can go 5 or more miles without a stop.

It's fun to have so many bikes to compare!