Other than the Placebo Effect, don't expect miracles in speed improvement. Tire rolling resistance is the result of a number of factors of which tire cross section is only one. Contrary to mythology the narrowest section tire doesn't always have the lowest rolling resistance. For some, depending on rider weight, the lowest resistance, and best handling is with slightly wider tires.
I'm not saying narrow isn't good, just that narrowest isn't always best.
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