I will be buying one of these real soon. I shoot portraits and weddings. I use a tripod alot but do candids as well. I have reviewed alot on various tele's but need more specific feedback on these two. Basically, I'm trying to judge between gaining the hand held benefits of IS but losing apeture to 5.6 at times, verses a consistent f4 with more sharpnes and clarity with the L. I want the closest I can get to the latter in my Elan 7e system. I have the 28- 135 USM IS but am not real impressed with the sharpness and clarity. (Have truly enjoyed the ability to hand hold at 1/15 tho.) Local camera store said to go 'L'. I wish I could have it all with the 'L' 2.8 IS but do not have $1800!