& then there's - doesn't matter how fast we go, we'll always want to go faster ...
also, sometimes a measured speed increase is not as important as the perception of feeling faster
so when you switch, go to a "road" tire. meaning a tire with lower rolling resistance (& higher TPI) & if you're staying on pavement maybe go to a 25? there's a dedicated Trek FX forum/thread where some of those guys might have something to add
FWIW these are the tires I have now, for the road, got them based on reviews & info I got here on BF. I like them very much. I feel quite swift & they are not harsh or twitchy at 700x25
Michelin PRO4 Endurance Bicycle Tire 700x25 Black