The pros and cons to each are mostly minor things and come down to personal preferences. I have both and prefer the smaller, lighter Z8. Do you prefer the larger gripped body or do you want a smaller, lighter body to compliment it? How important is built in gps? How important are matched card slots? will it be an issue carrying two different types of batteries and chargers? From and operations standpoint, other than vertical grip, the main two differences is the Z9 has three front function buttons instead of two and a drive dial under the mode dial so very similar.
Your replacing the D850, in that case a Z8 shouldn't be an issue being slightly different to the Z9, more so do you even really need a Z9 or could 2 x Z8 be more than enough for all your needs anyway ?
If the choice is a Z8 with Z9 or two Z9 units i would go Z8 Z9, I mean a
Sony A1 is 747 G and tiny, a Z9 is almost 1.4 kg and massive in size.
For some at times we have to many choices.
Forums like this really help with members sharing first hand experinces in many different applications, we can learn so much, be it cameras, lenses, technique, making decisions choices and compromises.
I think it depends on who we are, what we do, or want to do, combine this with means if applicable, it all helps to melt the pot into a clear broth.
Looking back D3X D3S, D5 D810, D6 D850, all seem to be more seem;ess togeather, over time the differences have widened a little especially in mirror less cameras.
TODAY, the fundamental combination of time light and speed is still there in all cameras and it has been since the beginning of time, AI is going to or should i say may change that for developers and creators be it stills or video. We will in the main stream market do in video what we used to do to stills using PS LR.
The answer as to choosing a Z8 or Z9 is simple the D850 was a back up with a huge difference to the z9 so the z8 should be almost seamless. especially as a back up...........or second camera is what i am getting out of all this ..............
Some Key points.........
Rent a Z8 for the weekend, use it along side the Z9.
As some of my friends have done they have sold their Z9 and bought a couple of Z8 at the old prices that ran out in end of February this should be more apparent once the pipeline sells out.
If you have tolerated the D850 with the Z9 and the synergistic differences a Z8 is not an issue.
I know many that love and equally hate the combo, however its dictated more so by what they do.
For cost if an issue there are plenty of cheap used Z9 units for sale.
I just picked up a NEW Z8 at used E BAY market prices, so i am ahead of the first full wave of depreciation, selling my Z9 i got out of it unscathed as i bought it right, for me the money is made in the buying not the selling.
Left field option,
why not go 2 x Z8 units after selling your Z9 unless your doing a lot of video think about it.
What is it you really need the second camera for, a good point ?
If weight, size and funds is not an issue and you do a lot of video then go 2 x Z9, if it is then you have the answer to maybe compromise a little if at all and go the Z8 Z9 combo.
Your replacing the D850, a Z8 shouldn't be an issue being slightly different to the Z9, more so do you even really need a Z9 or is the Z8 enough for all your needs.
If the choice is a Z8 with Z9 or two Z9 units i would go Z8 Z9, I mean a
Sony A1 is 747 G and tiny, a Z9 is almost 1.4 kg
Only an opinion if it helps