I have an NP-F battery plate on top of my BMPCC4K cage and with an NP-F970 equivalent battery (IDX) and a genuine Canon LP-E6N battery inside, I get four hours of continuous 4K DCI recording at 5:1 compression.
The NP-F option is way lighter than a V-lock and you can use various size NP-F batteries to suit the occasion, plus it gives you hot swapping capability. I would think you could do the same with a BMPCC6K.
The benefit of my setup is that I can put the entire rig, cage, monitor and all on a Crane 3s gimbal (with focus and zoom motors) and it works perfectly.
The Sony Z90 looks solid, particularly with the xlr mic inputs. I should have mentioned that variable frame rates to include slo mo is also a preference. Thus the BMPCC6K with up to 50 fps 6144 x 3456 video looks nice and HD up to 120 fps. With a v-mount battery it seems to get just shy of 4hrs run time. If it can take the heat that looks like a good option. I also like the CFast slot.
Then I also see the Z CAM E2-S6 Super 35 6K Cinema Camera which shoots up to 6K at up to 60 fps, DCI 4K up to 75 fps, 1080p up to 120 fps. Not sure how it performs in 40+C.
I've used my BMPCC4K continuously in 40+C Australian summer heat without any overheating issues. I suspect that the BMPCC6K would be just as capable. Both are very reasonably priced cinema cameras that produce fantastic results (in capable hands, mine are still all thumbs). The MFT format has it's advantages, as you can use just about any lens ever produced (using an appropriate adapter) and, with speedboosters, you can get almost a full frame look.