UPDATE
I recently took two other bikes out for average mph comparison. On both of those bikes out (one is a hybrid, the other is a road bike), I easily maintained an average of 11 mph. Had I pushed a bit harder, I could have easily hit 12-13 mph. Even 15 mph.
I am going to take out the Giant Escape Disc 1 again, and use the same GPS tracker. If the problem is simply the design of the bike, I now have two different bike types, and GPS data, to figure this all out.
While speed is not necessarily my goal, figuring out what each bike can do when I am utilizing "about" the same wattage of leg power will help me when choose which bike to use between a leisure ride by the ocean, or going on a longer excursion that would necessitate knowing when and how to prepare for rest stops, or extended layovers.
But in reality, the "feel of the speed " on any of these bikes seems identical to me. At least now I will have data from various rides and bike types to compare.