We have used both, but the questions regarding difference in output quality are so infitesimally small and nearly always down to personal perception. For every persom who says the Mark 1 let alone the Mark 11 surpassed medium format there will be someone else who says it doesn't. The reality is your customers could care less about such minutiae and simply want their precious momemts captured as skillfully and unobtrusively as possible.
The great wedding photographers were doing great digital work with a few million pixels let alone nearly 17 million. Its not about the pixels its about the pictures.
Professionals simply face a workflow choice digital or film. Digital is expensive but in todays business economy (particularly weddings)we would find it impossible to construct an arguement for film. If your producing fine art work and you are that good that(ie world famous) galleries wait for your output then yes plate cameras and big negatives cannot be beaten but who really operates in that rarified place.
If you have no digital experience the cost to your business will be much much more than the cameras and lenses. You need a lot of good software, computers, hard drives, top class color calibrated monitors, back up media, catalogue systems. You will need to develop new workflow methods and train to use all of the above,as well as the new camera systems. The shots you may see in magazines, media etc from the MKII don't come out of the camera like that, there is a lot of work with all of the above to get those results. Before digital you were a photographer now your also a lab. The time cost will be very high and it may take your business several years to absorb those new costs.
Hope the above helps with your costings and comparisons
I have lusted after the (all hail!) EOS 1Ds Mark II for quite some time (haven't we all?). I'm interested in hearing from others who have used BOTH the 1DsII and medium format cameras, preferrably 645.
I'd like to know if the Canon is suitable as an equal (near-equal) for MF. I'll need to purchase one or the other for wedding work later this year. By the time I consider the price of a MF body, lenses, etc. I'll be within throwing distance of the 1DsII. I'm willing to pay the extra $$$ for the instant feedback of digital and to use the lenses I already have for my 20D. But ONLY if the resolution can meet the demands of typical wedding enlargements.
Comments on you real-world experience is greatly appreciated. Thanks guys.

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