I missed an older post, so I’ll answer it first.
DY – Do you think Litvish girls with Chasidish boys is a more palatable or appropriate scenario than with YU boys?
That depends on the individuals involved, but my point is that in the vast majority, both won’t work because of the cultural differences, even if we ignore the “frumkeit” issue.
Neither a so-so ability learner (who is putting his fullest into his learning) or a strong abled learner is an am ha’aretz. So this am ha’aretz business has nothing to do with the discussion at hand.
That’s actually relative; I didn’t mean it as an absolute, I was using this statement of Chaza”l to show that how well someone learns is a direct factor in his development as a ben-Torah.
If someone of “so-so” ability will really learn b’hasmodah, with proper bikush haemes, he will eventually learn quite well, in fact better than the lazy genius. If a boy doesn’t yet learn well, his development will be, to some degree, behind (if he’s a harder worker, he’ll eventually catch up and surpass those of superior talent).