
Sorry but from the start this whole thread seemed to be for justifying buying a higher end camera opting out the 6D just for the shutterspeed.
I can think of lots of reason to buy the topoftheline model shutterspeed not being one of them
The simplets reason is pure lust, just because this model appeal to you in it self and that's more than enough. There is is no reason to try rationalising.
You already got two bodies and are buying the third so for the odd once every other year occasion you might encounter those lighting situations a simple 2-3 stop ND mounted on a lens on one camera body could solve that "problem"
I want the Fuji X-T2, not because its weathersealed, got 1/8000 ss or better lenses or IQ but simply because it appeals to me and I like the handling of it.
I could bring a gazillion arguments and this forum could tear them all apart except for the one
I WANT IT and that's really the only argument you need.