Also, low SCs like 45s and 67s *should* be considerably less profitable than QJs and T9s because:
...
2) better 1-pair, 2-pair hands occasionally

Bear in mind, though, lower cards are more likely live, and I will often bet any pair I make on a low flop against a pre-flop raiser. with QJ or similar, you're much more likely to be dominated but you have a "better" hand in an absolute sense, which makes it harder to get away from.