The Z800 is a big lens, even though it is relatively light. For travel and money no object, I would buy a 600 pf and use a 1.4x TC if you need longer. I would then take the 100-400 as well. As I have the 180-600, that would be my choice, but it all depends on what you are shooting, how close you can get, how far you have to go carrying the gear and what light is available. If it is always low light, you may want to get the primes, otherwise the zooms will do.
Possible combinations:
A Z800 is 2.40kg and a 180-600 is 2.15kg = 3.55kg. Covering from 180-600, then 800mm.
A 100-400 is 1.45kg and a 600 pf is 1.47kg = 2.92kg - add the 1.4x TC @ .22kg = 3.14kg. Covering from 100-400, 100-560 with TC, 600mm and 840mm.
A 400 f4.5 is 1.25kg and a 600 pf is 1.47kg = 2.72kg - add the 1.4x TC @ .22kg = 2.94kg. Covering 400mm, 560 with TC, 600mm, 840 with TC
A 400 f4.5 is 1.25kg and an 800 pf is 2.40kg = 2.65kg - add the 1.4x TC @ .22kg = 2.79kg. Covering 400mm, 560mm with TC, 800mm, 1120mm with TC.
So, with the combos above, you would have to make the decision of how much weight you can and are allowed to carry, not to mention bag sizes.