a cruiser frame in and of itself will not slowyou down- its the wheels, gearing and componentry that will.

derailluer cruiser frame, alloy MTB wheels, 1.5 to 1.75 slicks and you will have a very fast bike who's look belies its abilities at speed.

Several of the current Schwinn cruisers, with a small upgrade in wheelset and tires, perhaps a nine speed mtn drivetrain, will give you a very very speedy ride.