I have been looking at buying this lense and a 40d to use along with my current 5D and 24-70 f2.8 for wedding photography.
Any feedback on this combo would be very much appreciated
I don't know whether such a long focal length (equivalent to 112-320mm) is suited to weddings, but I can say that the f/2.8 lens will let the 40D do high-precision AF whereas the f/4 version of the lens will not. That matters if you are shooting at or near maximum aperture. Otherwise the f/4 IS version is smaller, lighter, sharper and cheaper.
I am not happy with my 40D AF performance. It is nowhere near as reliable or consistent as my 20D, 1D2 or 1Ds2 but at least it works better in low light. Too often my 40D grabs focus on the wrong thing when only the central AF sensor has been selected and when that sensor is on the required target. Canon Service reckon it is working within spec. Most FMers will say it's my fault but I disagree. My 20D was more consistent than my 40D is, so it is not just that I am used to 1-series AF.
Something in MY 40D is not good even if it is supposedly "right". I'll replace it with a 5D or whatever replaces the 5D. In the meantime I'll "make do" with my 1Ds2 My 40D is not up to the required standard for commercial shooting.
My 40D is not up to the required standard for commercial shooting.