Well I'm back with some data. I was only able to do this commute 4 times with the backpack on the rack so far, so keep that in mind when I make my claims. There has also been a lot of storms in the area which have changed my typical riding conditions, wind speed and direct have not been constant with all 4 rides. Ok so for the first ride 39min, second 35min, third 34min, and fourth 37min. For the first ride I was being cautious with the rack and getting used to riding with it so that could attribute to my slower ride, the fourth ride was against an untypical strong headwind; but these time are still under my slowest time with a backpack on back. These times where pretty common of what I do with a backpack on back, though maybe a tad bit slower total time.

Though overall ride time may have increased slightly which would need more trials to confirm there are several notable differences between the two riding system. With the weight on the rack handling changes significantly, acceleration is a lot slower but top speed seems unaffected, it is less maneuverable, however the bike is more stable and there is less bike movement when pedaling hard and out of saddle. The main benefits I see for my riding conditions, flat terrain with high winds, is a 2-3 mph increase when battling headwinds. Also with the weight off my back I am more comfortable when riding and can focus more on my pedaling. My ride also is more enjoyable now and I seem to be less fatigued after riding than usual.

So my consensus is that riding with a backpack on a rack has no significant difference in total ride time than with a backpack on back, more testing is needed to confirm this claim. Against a headwind the rack is notably faster, but with a tailwind I think backpack will win because it catches more wind. I have no data for hills so can't apply that here. For me I say the rack makes the ride more enjoyable for my conditions.