Sali David

I would recommend the same to you :) especially in the sports area you already have a better result with the 5d.
I'm also thinking about upgrading to the Mk4 but I don't see the point. I'll have to think about it, maybe you'll be interested in my mk3 ^^ It "only" has 16000 resolutions. ;)

It depends on what you are looking for and what you do. If it's only FF and you do more still life, a used 6d would also be an option. As soon as it gets faster (sports) I would go for a 5d because of the AF. If money is no object, the m4. If it does, the m3 and one or two nice lenses. You'll need new ones too, I suppose.... Greetings

@Danielzupp
Unfortunately, the successor always makes the predecessor worse. If I only had mediocre lenses, I would think twice about the new super sensor (Mk4). What good is it if the sensor resolves 3000 lines and the lens only lets 2000 through.