Which Surface Produces Faster Times?

Bummmmmmmmmmmmp.

Physics would tell me that the road would be faster if all other conditions were the same. The road is a harder surface, therefore less of the force you put into the ground is dissipated.

Think of it like running on the beach- running in the softer sand is much, much harder and slower going because a lot of the energy you are generating is going into moving sand around instead of pushing you forward off of it. On the harder wet sand, less of your energy is lost to the surface, so it is easier to go faster.

Physics tells me the WR for both 5K and 10K is quicker on the track than the road.

This would be a good place for the Concrete Runner to chime in and give a really good science lesson regarding hard surfaces.

I was considering that as well--but spikes sink & push off more on a track.

It's not just energy return of the surface. One major difference is the availability of splits on the track, allowing athletes to get locked into the desired pace/rhythm. On the roads, timing information is infrequent. The track surface is (at least on a IAAF qualified facility) totally flat, while a road is at least somewhat undulating, which increases energy cost at least somewhat.

And, with the exception of a couple like Carlsbad some years, top-tier track events simply attract better quality athletes.

Harder tracks are faster, so I would assume, in theory, that concrete/asphalt would be faster than rubber. Previous ppl have pointed out that is other features of road courses, not the road itself, that lead to slower road race times.

Some other questions: what about a 400 meter asphalt track? I know they have these around, but what sort of times might come off of one of these if top talent ran on one? Or what factor might footwear play (spikes on a track vs flats on a road)?

Mondo is a relatively thin layer of material on top of asphalt. Also, it is not just absolute hardness that yields fastest times. Human limbs seem to respond best to a fairly narrow range of compliance, at least according to published research. It varies from sprints to distance, and also from short sprints to longer sprints. The compliant track at Harvard is often cited as an example.