and Is the speed of the Digic5 processor that much fast that makes people and photographers feel upgrading their old "Digic4-equipped" camera to the one that has a Digic5 processor?
Not the speed is interesting, the High-ISO Quality is (at least for me) the much more interesting.
Also i really hope that the DIGIC5 have a higher dynamic rate than the DIGIC4. Even the Sony Alpha 580 (which cost only 400 € and is not the newest) have a much higher dynamic rate than my 60D.
So if i would not have a camera than either i would wait or (please dont be angry) would by a camera from a different vendor.
To say the truth, there are so many competitors, the largest are Sony and Nikon.
If you buy the newest camera today, you can be sure in 3 months the competitor brings a new camera which is better than the one you bought. And if you sell all your stuff and buy that camera, in 3 months that will happen again.
Its a run you can not win so if you really _need_ a camera and it should be a canon, buy one with a DIGIC4 and wait until DIGIC6 appears. Some people keep there cameras for about 7 years and i think the DIGIC6 will come sooner.
