Now that POTN/AMASS has a forum for medium format digital, I thought I'd provide some message traffic for the nascent forum! I need to justify my new title bestowed upon me by Pekka!
I have been keeping a table of camera sensor size and resolution for FF and APS-C cameras for a long time. I decided to update that table with Hasselblad and other medium format digital cameras and digital back add-onsn offered in 2014, with some slightly older models included for reference to compare against the current products.
The reader needs to keep in mind that optics is a very important factor in resolution...one CANNOT assume that a 40% pixel resolution in one direction will necessarily result in 40% better detail resolution. For example, if we double the pixel count on APS-C cameras, from 8Mpixel (350D) to 15Mpixel (50D), we see detail rise only 34% (2640 vs. 1835 LP/PW) with the 70-200mm f/2.8 lens.
With 15Mpixel FF body, photozone.de published tests of 70-200 f/2.8 IS vs. 70-200 f/2.8 IS II lens shows relatively comparable performance at 3444 vs. 3469 LW/PH (line widths per picture height), a measure of detail content within the frame delivered by the two generations of 70-200 f/2.8 lens. If we put the 70-200 f/2.8 IS II lens on both 50D and 5DII -- both 15Mpixel cameras -- photozone.de tests show that the 5DII provides 41% better detail content using the same lens, in spite of having 20% less pixel density on sensor (FF=3469 vs. APS-C=2460 LW/PH) simply because the FF sensor has more total area to capture what the lens can deliver per millimeter at the focal plane! Size matters...look at the number of lines which can be theoretically resolved by a sensor, after it has been enlarged to fill a 16x20 print (Column J)
As hobbyists or even professionals, we have to consider cost of equipment -- unless we are independently wealthy. Is the cost differential of medium format digital 'worth it' compared to the performance increase we see? Dunno, until photozone does LP/PH measurements on medium format. That ultimately is a question which has a different answer for each of us. The pursuit of performance with medium format digital (vs. FF 135 format) is a whole lot different now than when we did an analysis of the advantages of medium format film cameras vs. 135 film decades ago, due to the cost increase with size of format.