Is it raining? What wheels am I running? How are the aesthetics equal (would the caliper bike have decorative rotors and the rotor bike have decorative calipers), and related, what style of frame and headset are we using, and what is the color scheme? What are the particular brakes? At what altitude is the 1.5lb difference measured, and where will I be riding the bike? What am I using the bike for (i.e. racing or solo riding or cooperative pacelining)? What tires are being used? Does the bike have full-length fenders? Is the bike just being used on the road, or is gnarly off-road descending in its future?