I will give some pointers from my experience in Australia, but can't guarantee this will be the case globally!
1 - I won't say no but moving across would certainly not be common. McKinsey Implementation operate in very different scenario's to regular consultants, and also have a very different skilset. However McKinsey is a very dynamic company so if you really want something to happen there is normally a way to make it happen - it just won't be easy
2 - The profile of most MI entrants is very different to generalists, and they then build a different set of skills more focused on driving organisational change, so the exit opportunities are therefore quite different. Ops probably falls somewhere between the two. You will find it harder to move inot PE or hard core strategy from MI, whereas you will be better positioned than generalists for a corporate management or transformational role. Depends what you are after
3 - Without going into detail rem is comparible, but bear in mind at the same grade someone in MI will typically be more experienced than a generalist consultant
Hope that helps