Hi Thomas, you're forcing my hand a bit. It's only been a couple days with the ZD and I don't want to say anything definitive yet. So, I reserve the right to completely flip-flop
When it comes down to file quality, I would not sell the ZD camera for a P25. Some initial impressions:
1) P25 was cleaner at ISO 50. The ZD looks slightly better than the 1Ds3, and not quite as good as the P25. This depends alot on the lighting conditions and what type of post processing is applied (pushing around shadows with levels editing, etc).
2) The ZD color is a bit more muted. Quentin's picture above shows that great color is under the surface. I need a month or two for figuring out how to maximize the color potential. The P25 had punchier color, but it always had a reddish bias. Sometimes a couple ticks on the magenta WB slider would take it out, other times the red ran through the entire file and post processing would unearth more and more red. The Kodak and Dalsa sensors have different color personalities. I also have a lot of Aptus-22 raws on hand, and I think I prefer the color sensitivity / response come out of the Dalsa chip compared to the Kodak.
3) I'm pretty confident that the ZD is beating the 1Ds3 by a wide margin when it comes to highlights. I feel like I've gained 1+ stops in the highlight range (compared to the 1Ds3). Compared to the P25 the DR is probably similar. Usually the P25 files need the lower levels raised on landscapes. With the P25 it was a good idea to meter for highlights, and then boost the shadow tones in post processing. ISO 50 was really clean, so that worked well. With the ZD, it SEEMS to take a brighter picture. i don't feel the need to boost the mid and lower tones. And it's holding highlights well. So, I think Mamiya's tone curve is biased towards getting more DR above the midpoint and they are foresaking some of the shadow detail. So far the ZD seems more workable for how I shoot. I really don't worry about clipped highlights thus far. But again, this is just the first impression, so opinions may change.
4) The sensor cast from the P25 was horrible and every file needed a LCC correction. It had the typical "Italian Flag" - greenish bias to the left, magenta bias to the right. That drove me crazy. LCC would fix 80-90% of the cast, so the net result was fine. Thus far I have not seen any signs of sensor cast from ZD. I'm sure there is some because that's the nature of things, but at least it's not jumping out and pissing me off.
5) I've tried ISO 100 alittle, seems okay. I think I'll side with Quentin - I doubt the camera will move off of ISO 50. He has the D700, I have a 1Ds3. If I needed ISO, I'll go with the Canon. If I'm happy with the ZD, the 1Ds3 will be sold and replaced with a 5DII.
I doubt I will ever go back to a P25. Yes, the files could be good, but the system came with alot of headaches. Used prices have come down considerably, but I still don't think I'd do it. The ZD camera has some brilliant features - like the multipoint AF. The AFD III probably has the same set-up. I probably wouldn't go back to an AFD II.
If I were "moving up" from a ZD, something like a H3DII-22 really interests me because I prefer integrated approach - things like a single, common battery; the LCD screen for setting the camera options, etc. For me, moving up really only buys better ISO performance. And as said earlier, if I'm going to move into the upper ISO ranges, I'd rather shoot a dSLR.
If Nikon comes out with a MX system and the ISO and AF performance is there, then that system will be very interesting. There's no way on this planet I'm giving Leica $18k for their S2. Its ergonomics & menu dependency are not well thought out. If Leica re-thinks some aspects of the S2 and gets the price in the $10k range, then I'll give it a hard look.
In the end the ZD camera is a really cheap way to shoot medium format and it will probably deliver 85-95% of the P25 / Aptus-22 quality. The P25 / Aptus-22 files are presumably better, but the ergonomics (integration) doesn't match up to the ZD. If Mamiya updated the ZD camera with a quasi modern LCD and faster, more responsive throughput, I think they could torpedo the S2. And if slapped a P30+ sensor in there, then they'd really put Leica on its heels.