Factory Camshafts ~ 1968 340 '4-Speed' vs. Chevy '151'

I have allways wondered about those "375" horse 327s, I know people talk about they were so awesome and all, but they made 100 more HP than the 340? or the same HP as the 440 HP? I dunno, it seems like I remember a magazine article testing head flow, and those double hump heads were no better than a X head....