I should have said I can't tell much of a difference in performance and efficiency. The biggest difference I have noticed is that when I get tired it's easier to pedal circles with clipless, and that difference is negligible. I have 3 road bikes. Two of them have had platforms since I built them. I just switched one of those two over to clipless. On my regular 30 mile ride my average time remain unchanged. FWIW I am a casual rider who averages 16-17 by myself. It may also be worth mentioning that I live in the flat lands. That said, my platform pedals have served me very well in two trips out to Colorado. This is a touring forum, so I should also add that I have never done any loaded touring. When I finally go on tour I will use platforms for several reasons. I am a stop and smell the roses kind of guy. I'll spend quite bit of time off the bike. I also much prefer platforms when I get into urban areas. I find it's much easier to get going from traffic lights with platforms.

In short, if you read the many articles I linked that assert there's not a tremendous advantage to clipless, that has been my experience for my kind of riding.