Who likes their 400mm E FL over having a 300mm 2.8 or 500mm E FL? I've got lens lust for a 400mm 2.8 E FL and have the opportunity to buy one used. Trouble is I would have to give up my other 2 lenses to get there. How heavy is it? I can carry my 300mm or 500mm all day if needed. The 400mm is a little heavier but I'm not sure how much. I can use a strap and monopod but not sure how practical it is with this lens.