Planing end grain is not an easy task and getting a nice result should be taken as a good indicator of sharpness, especially in softwoods.
It's impossible for most beginners and very difficult for a lot of learner woodworkers to get good results planing end grain at every attempt. And it seems paradoxical but the end grain of hardwoods is generally much easier to plane than that of softwoods, which is one of the reasons that working with softwoods is actually quite challenging.
I've sharpened my plane to a degree which I think should be more than satisfactory (up to 6000grit).
Final grit isn't an indication of sharpness.
Finer grits do tend to produce a more refined, ultimately sharper, edge but it's quite possible to hone on a fine waterstone or ceramic stone and for the tool to still be blunt. This can be due to poor technique, or the incomplete removal of the previous wear bevel (something that is surprisingly common).
And it's possible to produce a superb edge on a stone much less fine than this — this was actually still the norm only a generation or so ago, when very fine stones were still not commonplace in Western workshops.
If it helps you might like a quick read of these previous Q&As:
How can I tell if wood turning (lathe) chisels are sharp?
Is the "paper test" actually relevant to sharpening chisels and planes?
However I am getting a lot of tear out when the plane gets to the edge.
This is perfectly normal. As you say there are some tricks to prevent this, as covered in an early Question, How do you plane end grain?
but my real question is - do better grades of wood, especially hard woods, fare better or worse in this regard?
Splitting out of long grain, also called spelching, during planing (and sanding) of adjacent end grain is common to all woods and some hardwoods are actually worse for it than softwoods because they're very stringy, or brittle.