i guess it's too hard to generalize without specific tires, widths and pressure. interesting link - but i guess what c-note was asking isn't possible to extract from that article exactly:
"A direct comparison is impossible though, as the tires have different widths and some are used with very different inflation pressures."
but many tests show that width just widens the contact patch while a narrow tire lengthens it, so not much difference, and if anything wider can be better. so with a smoother tread, you may be faster on both accounts. of course, there has to be a limit. a 2.5" smooth tire having less rolling resistance than a 25c? that'd be surprising.
c-note - how about some testing? i'm sure readers would be interested...