What's a good tele lens for the Canon S1 IS out of those two? What are the major (besides the zoom ratio) differences between those lenses? Which one has the least vignetting at wide-angle? I would like to be able to use a major portion of my camera's optical zoom with the lens attached. Also, how close to those lenses can you focus? I may be occasionally attempting to use those lenses to take a shot of someone's eye (and have it nearly fill the frame) at a considerable distance.
Also, how far away (assuming full optical zoom (no digital) on the S1 with the lens attached) would you expect to be to take a head+shoulders+bust+torso shot of someone? For example, with full digital zoom at Petco Park in the left field seats (probably about 300-350 feet away) aiming toward home plate, the batter's full frame (head to feet) took up about 1/2 of the height of the frame.