I don't doubt you improved by 5 or 8 minutes, whichever.
I doubt the gain was made due to your bike as you claim.
That's where I call bull****.
And 675 feet over 21 miles is not climbing. I can do that here in Illinois. Illinois is flat as a pancake.
Now I have to call bull****. I've lived in Schaumburg, Arlington Heights, and outside of West Dundee, IL. There are no hills in that area that are comparable to what's in this area. I have a 50-34 crank and an 11-32 cassette, and I use the full range every ride. When I lived up your way I had the same steel bike I mentioned in the original post, and used about three gears: One for no wind, one for upwind, and one for downwind, just about the same three gears I used when I lived in St. Petersburg, FL.