Is the Pentax 645z at $8000 a realistic comparison to a $3600 DSLR?
Of course not, but if you're already leaning toward buying a 645Z, but the 5Ds ends up offering similar performance (which I doubt) for a fraction of the cost, then it is absolutely a valid comparison. Plus, the feature set (AF, FPS, weather sealing, peerless high ISO, flippy screen, outstanding shutter dampening) of the 645Z allow using it in settings and situations where MF previously wasn't even an option, which makes the comparison even more valid. As far as lenses go, you'd be shocked how reasonably priced the legacy Pentax MF glass sells for on ebay. That said, there are probably very few people what will cross-shop these two bodies. I'm just weird like that