Here we go again.... I went through the exact thought process myself. Good luck in your decision!
Here's what helped me decide.
Make a list of what you want now (realistic list, please) and price it out for RB and RZ.
Make a list of what you want in near future and price it out for both.
Make a list of what you could want in a few years and price it out for both.
RZ is lighter than RB but not that much. 7 pounds per kit or 6 pounds per kit. Does it make any difference to you?
RZ has more plastic than RB but does it matter that much? Probably not? They are both professional level equipment.
Sure, RZ can accommodate a metered prism but can you afford it? I decided I don't want it.
Everything else is just preference. Except for 50mm, you can pretty much get the same lens for either body.