My daughter just turned 12. My bike was purchased so that I could accompany her on longer rides that she wanted to take instead of just going round the block. I didn't expect to enjoy riding as much as I have.
This last ride - my first long one under good conditions since the tire swap - shows a 1.5 km/hr increase in average speed.
Tough to know what to attribute to the tires, though. I am slowly improving over time - and the speed increase has been gradual but measurable (and yes, I am using a GPS computer). This is probably the largest single increase I have noticed, even if it only amounts to around 1 mph. Then again, this was also the longest ride I have done to date by 10km, with a bit more climbing (though still fairly flat overall) - so a even an single mph increase in average speed is nothing to sneeze at, as it was carried over a 25% greater distance.
Seat of the pants tells me the bike is quicker overall, and definitely more nimble. Nothing in the numbers contradicts that - and confirms it to a degree. The unexpected result is that the ride is also noticeably smoother - which both completely counter-intuitive and a pleasant surprise.