I'm not thinking about skinny wheels. Just normal wheels which have varying widths. I would suspect that wider wheels would be slower. That there's more track contact probably isn't much of an issue since it's mostly rolling. I did, however, have some corgi juniors as a kid that despite being very light and having pretty small wheels were very fast. The only notable difference I see in them is that the wheels have a ridge stripe in the center which is the only thing making track contact. Like a lot of the MB/HW knobby tires. But then those wheels, despite that small stripe of track contact don't generally perform well.
What I would suspect makes wider wheels slower is the greater amount of axle contact and hence friction.
Anyone have any thoughts or experiences or testing to share on the subject?