Runnng 25mm Durano`s and they aint slowing me down in fact quite the opposite. In fact my tyre of choice is usually Mich Pro 3 or 4 in a 23mm but if I buy new ones i think i will try 25s. Wish my fixed wheel could take 25s as I would be all over that size like a cheap suit. The ride quality is much better but alot may depend on your physical size. If you are a lightweight whippet then smaller tyres should be good, but for those carrying a bit more `muscle` then 25s FTW !