OK, I did an interesting comparison, and I wanted to share.
I have a Cannondale road bike that's about 5-6 years old that is my normal ride. I also have a 'new to me' 1997 Air Friday. I do the same basic ride over and over on the C'dale. I've been waiting for some parts for the Friday, which is getting prepped for travel duty. So, I got my seat, seat post, tubes, and Primo Comet tires delivered and installed.
I have an older cyclo-computer on the Friday that gives me speed/time/average. On the C'dale I also get cadence. They are different computers and since the tire sizes are different and I'm not 100% sure of the calibrations (I used Sheldon Brown's chart for both, blame him) that is a possible variable. I'm pretty consistent in that I like to spin from about 90-100 rpm. That's probably not a big variable.
The Friday has 62/52 front chainrings and an 11-23 8-speed cassette. The C'dale has 53/40 front chainrings and an 11-27 9-speed cassette. Gearing isn't a huge deal. I run both in the big ring unless I'm climbing and generally in the lower/middle part of the cassette.
So, my average speed on the C'dale for my 'normal' training ride is from 19.5-20.0 mph. I have averaged up to 20.3, but that was with favorable wind conditions. The path of the route I take tends to cancel wind effects, but there still seem to be more and less favorable conditions.
Today on my Air Friday I averaged 19.2 mph over 20.1 miles. I was carrying all of my normal stuff with me, so no real variables there. I did have a real tough workout yesterday that was 30 miles with 10 of those being _serious_ climbing miles. I definitely was not 100%. The wind was blowing in it's least favorable direction, but it wasn't really all that strong, so it didn't skew the data too badly. If I were going to guess, I would guess that on my C'dale today I would have averaged 19.5 or 19.6 mph.
So with a completely un-scientific analysis, I'd say that the Air Friday is about 0.3-0.4 mph slower than my C'dale over a 20 mile ride.
I will also say that there were a couple of things I noticed. The Air Friday is a much smoother ride. There is one section of asphalt that I ride on which has a rough, exposed chip surface. The C'dale gets a lot of aluminum buzz over that stuff. The Friday didn't even know it was there. There is another section on the ride that goes over some older pavement with small potholes, frost heaves, patches, etc. Again, the Friday was much smoother. The front might pop up a little over a patch, but the rear beam would completely soak it up. There are many sections of this second section where I'll stand on the pedals for an instant as I go over the bump. I didn't do this at all with the Friday. It just wasn't necessary. On 1 particular spot there is a compression bump at the base of a short, steep uphill. The bike really loads vertically at this point. I wasn't even thinking about it, but I put enough load in the Friday's beam that it made a hlel of a noise. I initially thought I broke one of the bolts that holds it in. Everything seemed fine for the rest of the ride, though. Just something to be aware of....I should have been on the pedals, not the seat for that one.
So there ya go. It was an interesting little experiment and one that I might repeat for scientific purposes. I thought y'all might be interested. If I have any parting thoughts, I would say that if this were a 5 hour ride instead of a 1 hour one then the Friday might have faired a little better just because of being a little nicer to it's rider.