There's an advantage in putting the lightest wheel up front. Front wheels are inherently lighter, so I'm speaking in rotational inertia and mean lightest rims and tires.

This has nothing directly to do with speed, but with handling feel. The front wheel sees more side to side motion because of steering in addition to the normal side to side rocking both wheels see. Having a lighter wheel in front therefore lowers steering input forces and gives the bike a livelier feel. It doesn't directly translate to speed or efficiency, but lighter feel makes the engine feel better and might pull out a bit more output.