I also tested both 17-55 2.8 IS and the 24-70 2.8 on my 50D. 3 people looked at the photos and the 17-55 produced a ted better photos. So until Canon does not come with a better lens for FF I will not switch to FF
Sorry, but that's a rather flawed comparison and if that's your only reason for not switching to FF then you're making a mistake.
Sure, the 17-55mm has better IQ than a 24-70mm when using both on a crop body
. The smaller image circle of the 17-55mm allows that. But to be fair, you'd need to compare a shot with a 17-55mm on your 50D to the same scene shot with the 24-70mm on a FF body. I've done something similar - 17-55mm on 7D vs. 24-105mm on 5DII - and the FF wins by a clear margin.
Lots of people say they're waiting for a FF equivalent of the 17-55mm f/2.8 IS. The thing is, they forget that the camera is part of the equation. In fact, there's already a better
lens than the 17-55mm for FF - it's the 24-105mm f/4L IS. Keep in mind that the crop factor applies to aperture (in terms of depth of field for equivalent subject framing) and to ISO noise as well. So, the FF-equivalent numbers for the 17-55mm would be 27-88mm f/4.5 - i.e., the 24-105mm is wider, longer, and faster, and still has 3-stop IS. Yes, you lose a full stop of light (the crop factor does not affect exposure), but if you need the shutter speed to be higher, you can just bump up the ISO since noise is 1.33 stops better on FF as well.
So if you're waiting for a 'better lens for FF' it's time to stop waiting!