Happy Z5 owner here too. Got mine used a few months ago with 24-50 kit lens, FTZ adapter, two extra third party batteries and a small Nissin flash. Also bought a PK to Z adapter and three M42 to Z adapters.
Also found two used af (F-mount) lenses.. 70-300 AF-P and AF-S 105/1.4 E . All those lenses are sharp as heck
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I too was a bit torn between Z5 and 6 but absolutely no regrets. FPS is enough, buffer is good and files are great! Not even missing the top lcd. I keep the rear screen off and if I need to see my settings I´ll press the DISP button, half press the shutter and screen goes black again.
I´ve set one user mode for old manual lenses, M-mode with a few tweaks to controls. AF-ON to 100% magnification, Fn2 to 200% and Rec button to non-cpu lens data for ibis focal length.
I'm pretty sure Z6 won't get any updates anymore.. Z5 probably will.