TJ, great article, thank you, it was nice to get all that info clearly laid out.
In your final but on paragraph you mention the limits of the APS, but I confess that the NEX-7 has caught my eye as a replacement to yhe G12 , a camera that was a big step backwards. Reading the blogs it seems that the lenses are the let down for the NEX cameras at the moment, but maybe Zeiss or similar will react to what I suspect with be their popularity, and make some great glass.
I cancelled my order for the new Canon on reviewing the specs, because it simply doesn't provide what I need and want, a camera to get close to bettering the H2 system (with Phase P65) at 100iso. I realize on this board I'm in a huge minority who only care about peak performance at 100iso, but it is pretty much the only iso I'll shot at, and if the lights low I use a tripod.
I'm hoping the new Sony/Nikon 36mp sensor will provide what I want, fingers crossed.
For compact cameras, as for DSLRs, my choice has always been driven by max expected print size: I try to avoid interpolation as much as I can.
For me 5x7 inches print is the standard for casual shots from compact cameras, that's why I settled for a Sigma DP2x, as it sports the best sharpness and noise for that size.
NEX series cameras have great sensors and compact bodies, but they are aimed for larger prints; lenses however are pretty bulky and often compromise the portability of the system.
This is true also for other mirrorless compact systems.
What they lack is a relly good series of pancake primes in different focal lenghts.
About your specific requirements in low iso shooting, I don't think a CMOS full frame DSLR will ever get close to your actual medium format system.
The Phase One P65 is a very good digital back and a good match for quality medium format lenses.
Quality medium format lenses generally have a peak performance at F 11; moreover DoF requirements will force you to shoot 1 - 1.5 stops down compared to 35mm, assuming equivalent focal lengths.
Following previous assumptions, top MTF 50% value for a real shooting scenario is about 55 lpm.
Top MTF values for the P65 + real quality lense would be:
Unsharpened MTF 50% 40 MTF 10% 78
Sharpened MTF 50% 70 MTF 10% 82 with k= 0.55 (boost) and r=1 (radius)
Taking into account the size difference of diagonal for the two sensors, the ratio to 35mm full frame is 0.64, which translates into following equivalent MTF values:
Unsharpened MTF 50% 62 MTF 10% 122
Sharpened MTF 50% 109 MTF 10% 128 with k= 0.55 (boost) and r=1 (radius)
(Warning: The above equivalence should be worth only as a rough performance comparison, as the MTF values for different sensor sizes are not directly comparable: for example when you print (or enlarge) to the same size a same image taken with two different sensors, you are really relying on different MTF zones for the same limiting lpm value in the print. It could be MTF 30% from the smaller sensor and MTF 50% for the bigger one, which will appear cleaner (still far from the visible noise level) and sharper (more contrast for the same detail).
It's different from comparing values for the same MTF 50% or MTF 10% levels.)
Even a 50 Mpxls full frame sensor 35mm with the best real lense would not deliver similar values, falling short of 20 lpm in MTF 50% and 10-15 lpm in MTF 10%.
Resolution would be close, but difference in sharpness would be quite relevant.
However, SNR ratio, Dynamic range and tonal separation would still be much better with the P65 back.
So, given your typical shooting scenario, your actual digital back is your best option.