I can only go by what wikipedia and other sites say re horsemeat being lean:-
http://en.wikipedia.org/wiki/Horse_meatTrue, though, I suppose horses could become pretty fat, just like cattle, if they are fed mainly on oats and grains instead of just grass.
No idea re protein ceiling. I just note that eating lots of very lean meats and no fruits does not harm me. Now, granted, I don't necessarily stick to this all the time, and sometimes have lots of fats or lots of carbs as well or instead, but there is no immediate sign of problems re excess protein even if I consume only lean meats and hardly any carbs for a week or two.
Eskimoes did not always have access to blubber, some had only access to lean caribou.
As regards fruit, it all varies:- sometimes for a week I eat large amounts of fruit, sometimes I'll eat no fruit at all. More usually, it's just a little fruit, here and there. If I eat only raw fruit for more than 2 weeks, I start getting problems with blood-sugar-levels(have only done that when I started rawpalaeo all those years ago), but that's all, since I don't continue eating all-fruit, these days, for more than a week.