Completely worth it? It matters who you're talking to and what they are shooting. In my shooting experience, there have many instances where I have been glad I chose the 24-70 L over the older 28-70 L. I shoot mainly events, portraits and sports on a 40D, and the extra 4mm gained at the wide end is, for crop users at least, a big deal in my opinion. Currently I don't use any lens wider than 24mm, so the 28-70 would have certainly set me in need-to-get-an-ultrawide territory. I find 24mm just wide enough for medium/large group shots, if I have the space to step back of course. Which is another thing about this lens - It's "just" wide enough on a crop body in my opinion. Luckily I haven't been stuck trying to squeeze an extra large group shot in to a 24mm frame on a 1.6x FOVCF body. I certainly hope that time does not come![]


But on full-frame, I find 24mm to be a great focal length. I have tried this lens on a 5D and 5D Mark II and for me, 24mm is wide enough for environmental portraits, group portraits and landscape images. I'm assuming that the noticeable perspective difference between 24mm and 28mm is less on a full-frame body, so you may be correct.


Also note that the 24-70 L is weather-sealed, and the 28-70 L is not. For me, weather-sealing is more of a security blanket than anything else. But I'm sure I'll find it handy sometime.