I am a pro and have used various tethered backs since 2003, the Betterlight, Phase H25(22megapixel) anf the Leaf Valeo 17wi(17megapixel). For my personal work, mostly landscape and urban stuff, I have been using a Nikon D300 with a 17-55mm lens. While I have been very satisfied with the D300 images, I was made aware every day at work how good the Leaf 17 back is, in comparison. From Ebay, after a year of searching, I obtained a used Leaf Aptus 22megapixel to go on my Hasselblad 503cw with an older 50mm lens. I got the back about 5 months ago, but have only done a few outdoor tests, back problems and lousy weather in NYC did not help.
I print to an Epson 7600 and the 'small' prints I make are 20" wide. In the case of the D300 - 20x13.5"high and The Leaf Aptus - 20x16" (a 4x5/8/10 proportion). Unfortunately I am old, with old eyes and at that size while I see a difference, it is not great, but younger eyes see a bigger difference. Once you go to a 20x30" or 20X28", the difference becomes much wider, more obvious. In film terms, a 11x14" print from 35mm panatomic-x (slow, fine grain, asa 25, I think) will be easily outclassed by a 11x14" print from a 4x5 neg(asa 125). The MFDB has cleaner, smoother, healthier pixels, that how I would describe or characterize it.
There is something very important to consider and that is shooting style. In my case, I compose in the view finder. I think I see a shot, put the camera to my eye and use the zoom to crop and decide if I have a photo. With the Leaf Aptus 22, I found that a tripod is necessary to gain the full potential of the back. This was in my head, needing a tripod, before I purchased the back, so it wasn't a surprise. The biggest problem was composing a photo with a fixed lens. All I can do is move forward or back with my feet, to change the composition and often this doesn't work, because the landscape you are in goes up and down. Two steps forward, can lower the photo by 2 feet and the shot is not there anymore. I was realizing that some shots were no longer there and what other lenses would I need to carry to get those shots back. If I carried the D300 and a days shooting yielded 10 good images, how many might the Leaf Aptus yield. I am guessing 2-3 images, so am I giving up too much to obtain the highest quality, especially if you consider that the Leaf might come up with the #3, 7 and 8 of the 10, I might get with the D300. If I was getting 7-8 images with the Leaf, that would be great, 2-3 is disappointing. I am not sure that I like the trade off, but need more time to do real landscape work before I can decide. I did try an overall photo to be cropped later, after all I have an abundance of pixels, right. I do not like working this way, I might get home and find out that I have nothing. With the D300, if images are not working, I might try many different angles and crops to get something.
This was a way of working that I thought I could handle, enjoy and be productive. At the moment I am not at all sure. These are the intangibles that rise up and bite us.
Good Luck, Brian