speed gains

Wanted to briefly share my experience/comparison here + a question.
I have a gravel bike that I have been riding with Schwalbe G-One RS (45mm). This weekend I changed to a Continental Grand Prix 5000 AS TR (35mm) as I tend to ride on tarmac, especially in the summer. I always ride the same route at the weekend (40km / 25mi) as I don't have much time.

Here is the comparison:

Schwalbe Ø 25-26 kmh (16 mph) / max. 42-43 kmh (26 mph)

Continental Ø 28-29 kmh (18 mph) / max. 48-49 kmh (29 mph)

Since I was always wondering whether I should get a road bike, I first wanted to see how close I could get (to a modern race bike) via the tires and possibly later via the aero rims. My current rims are 21mm high.

What do you think I can still achieve in terms of speed with new rims?

I've only been riding for a year and I'm aware that I can still improve with more strength and fitness, but I love deep sections wheels 😉