Thank you all for your good and detailed comments. I will certainly try to get my hands on of Hasselblad, Phase One, Leaf or others. I have heard others say that you pretty much have to learn photography almost all over to be able to perform well with these cameras.
@ jondave. Interesting that you mention the billboards and that they are not shot with 20MP cameras. Interesting because I have read in other threads on this forum that several have shot exactly billboards with as low as a 8MP camera, and I have also been told by friends of mine who are graphic designers, that due to the distance that the picture is viewed from, this might actually work.
@jondave, you make an interesting case on how the agency/adagency world actually works, but the reasoning that you recognize is partly to other attributes than IQ and the need for higher resolution, and,- or, IQ.
Neither was I aware that you could highspeed sync at 1/1600, which I would guess (of course having never tried it) would open up lightning to another level.
Thank you all for your input. Very interesting indeed.
BTW: I have for a long time had my eyes on a 1DX, but the recent rumors of a high MP camera has had a slight unsettling effect on my wishes, causing a dissonance between the wish for an outstanding camera with many FPS versus what I would suspect to be a brilliant camera with low ISO capabilities and an unparallelled (in Canon terms) resolution. Maybe Nirvana is on of each, until I win the jackpot and can supplement my Canon gear, with a MF + accessories ?