No, the Nikon isn't Medium Format, but it ticks all the other boxes of what you're asking for. With the budget and ISO requirements, I'm not seeing an option other than a used 645Z & lens. Toss in more cash and you're at the GFX price point. Anything CCD isn't going to work at ISO 1600 & you've already had the 40mp 33x44 CCD w/ microlenses.