I don't mind running at ratings, personally; as long as they're good parts, that's what really matters. That, and thermal management. Which, it sounds like they're the pricey kind, so they ought to perform well (high lm/W).
Last pricey ones I got were, let's see... Cree XTEAW-00-0000-00000HGE3. Far smaller than the old gull-wing-cylinder style they replaced, but their efficiency is so much greater, they still run cooler. It's... a little insane. And quite wonderful.
So, if it's already designed to run an acceptable temperature with older chips, or, like, resistors (i.e., assuming 100% applied power goes to heat -- in reality it's more like 50% now!), they'll run quite cool. If it's new design, and you're accounting for dissipated power only, or don't have much opportunity to dissipate heat in the first place (compact, enclosed?), yeah, derating may be desirable.
Tim