I finally put my Contax/P30+ combo into service tonight with an outing to Miami, Arizona for some nighttime photography. Unfortunately, the initial results are not very promising, as (IMO) the images started to become excessively noisy after just 45 seconds of exposure at ISO100. (I also had some problems with the Contax 35mm lens creating ghosts whenever there was a strong light source in or just outside of the frame, despite using a lens shade and despite using a gobo to further shade the lens from direct light as much as possible. But I digress...)
The ambient temp was in the low to mid-80s range and according to Capture One's handy chart, the back should have been good for exposures as long as several minutes at these temps. But either my tolerance for noise is lower than for most people or my back isn't performing up to snuff, as the noise levels I experienced with tonight's batch of images are clearly excessive.
Anyway, while I wasn't planning on upgrading to a P45+ just yet, if it's a much better performer than the P30+ for long exposures, I may need to look into this as I fear the alternative may be for me to punt on medium-format digital and (don't laugh!) return to the various m4/3 setups with which I have been surprisingly successful previously.