Only a wind tunnel test can give you a specific number, but the faster you go, the more important aerodynamics becomes. Honestly, most equipment gives you a tiny improvement compared to what you can do by just training properly. If you're getting these wheels because you want to add 2 mph to your average speed, forget it. If you're losing races by a fraction of a second, it's worth a shot. If you just want to get a good deal on some hot looking wheels, that's up to you.