Just to inform, loss of color saturation is a crosstalk effect. With crosstalk the color channels get mixed, that is evened out, that is closer to monochrome, that is loss of saturation. While crosstalk also will lead to softened detail (lower contrast between two adjacent pixels due to the mixing) it should be much less than the softening caused by the natural lens sharpness falloff. The visible contrast lowering should stretch one pixel, and lens softening is generally larger than that in the area where crosstalk occurs. Noise is due to the general pixel vignetting, color cast due to varying pixel vignetting.
The P45+ has the Kodak KAF-39000, and as I've recently heard from Enda the 50 megapixel (6um pixels) KAF-51000 used in Hasselblad CFV-50 and H5D-50 also performs well with these lenses, unlike the Dalsa 6um (IQ160, P65+ etc). Going from 39 to 50 megapixels may seem like a too small upgrade though (and you'll lose long exposure). For me that is on 33 megapixels it would be a suitable upgrade though. Actually I find 50 megapixels and the 39x47mm sensor size to be a very nice sweetspot of size relative to the common 90mm image circle (nicer than full-frame 645), and good resolution too. As my shooting style require f/11-f/16 there's not too much gain to go with smaller pixels than that.
As I have expertise in crosstalk analysis I'd like to further investigate the actual performance of the CFV-50/HxD-50 on these lenses, but it's hard to find tech users with any of these backs and lenses that can provide me with raws for analysis
. If it actually does perform well I'd say that the CFV-50 is a very under-appreciated back and it's a pity that it has not been more popular in the tech cam community, where Phase One instead rules. Hasselblad is totally clueless about tech cameras though, so it's their fault not showing it's superiority in tech cam use. And now they have discontinued it, and the replacement CFV-50c is near useless for tech wides. The H5D-50 is still current though, but not sold back alone (I assume). The KAF-51000 sensor is still current in TrueSense Imaging's product catalog, so anyone can still make new backs with it.
The critical crosstalk angle is unfortunately not specified in the data sheets, but if I compare angular response (indicates color cast, which is often related to crosstalk, ie more color cast more crosstalk) between the KAF-39000 (P45+) and the KAF-51000 (CFV-50) they look about equal. On the other hand Dalsa's 6um is not far behind so these diagrams don't say that much as they only look at quite narrow span. Dalsa only measure +/-30 degrees while Kodak/Truesense have +/-40 degrees in their diagrams, which might indicate that Kodak handles a wider span, but a stronger indication is that the Kodak lacks microlenses while Dalsa have them. I think the SK28 will deliver light at a 55-60 degree angle at the edge of the image circle.
The KAF-39000 support 39 degrees before crosstalk occurs (
http://www.optcorp.com/pdf/FLI/31Mp_and_39Mp_Full-Frame_CCD_paper.pdf). It should be noted that small amounts of crosstalk don't disturb the image too much, so pushing a little bit past that is not too bad (unless you're doing reproduction work where color accuracy is extremely important, but you wouldn't use ultra-wides for that anyway I guess). I haven't found any number for the KAF-51000.
Concerning sensor performance in ideal conditions the Phase One Dalsa backs is in measurements better than the Hasselblad Kodak backs, slightly better DR and better color separation, however that will be more than nullified on tech wides after LCC correction has been applied.