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Wouldn't even consider going back to a 40D,especially after the firmware update for the 50D.
50d Drivers & Software
Bought the 50D and sold the 40D...after about six months bought another 40D...once we did the firmware update,found my wife and I were each wanting to use the 50D more then the 40D...so sold the second 40D and bought another 50D so we each have one...
In AV or TV Mode you can get up to four stops either way...set the AEB to the function button,turn the main dial behind the shutter button to the four stop setting,take the first of the AEB three shots ,press the function button again and using the back quick control wheel to adjust the EC two stops for next three AEB shots and so forth....doing this to get 6-12 AEB shots.
Although I normally shoot M, you can use Av because in M in order to vary the shutter speed you have to use the the top dial which is not as easy and smooth moving as the back dial. I get a six shot spread by doing the following:
In C.Fn. change dial increments to 1/2 stop.
Set AEB to +/- 2.
First shot at 0 EC.
Two clicks of the back dial to +1 EC. Second shot.
This gives -2, -1, 0, +1, +2, +3.
Using a remote release in one hand and the second hand on the back dial, it takes not much more than a second.
You can set the AEB to the function button and have quick access to adjust the exposure compensation.By doing this you can take 6-12 bracketed shots.For more in depth on this read the link below and the folow up comments.
Canon 50D Auto Exposure Bracketing
A few links with alternatives for AEB bracketing with the 50D
Canon 50D bracketing for HDR
Single Image HDR