On the street, my Cannondale Rush 5Z with stock 26" knobbies rides like a typical mountain bike on the street -- difficult to maintain a speed, hairy on the corners.

I put 700x28 wheels & tires from my Bad Boy on it, and with the suspension locked out, it rode almost exactly like the Bad Boy (just a little heavier). Better cornering, better speed, etc.

I'm sure that I'd notice the same difference with narrower slicks on the 26" wheels.