First we have the racing bike. This one is on long term loan from my brother. It was sitting there in my garage with flats, so when a sale came along I took the opportunity to replace the tubes and tires. Actually the bright yellow striped tires makes it look even faster somehow--purple and yellow go together for racing vehicles. And it really is faster. Unfortunately, I don't have a controlled environment for testing, but when I rode it, I found that I passed pretty much everybody with ease, perhaps 95 percentile in terms of speeds on the trail, compared with 65 or something for the mountain bike. Also, here's the surprising bit. I expected to have no advantage going up hills, but for whatever reason, the geometric differences with this bike allowed me to comfortably power my way up hills in high gear, which I can't do on my mountain bike.
The mountain bike, however, is much more comfortable. Especially my back is much more comfortable when riding the mountain bike. But also my neck, my hands, my feet, pretty much everything else. One could argue that maybe this is just because I ride the mountain bike on a daily basis and not the racing bike, but I don't think I'd be able to ride the racing bike everyday. At this time I still have a strong preference for the mountain bike, even though it's not as fast.