Modest quibble: the f/1.2 lens is a half stop brighter than the f/1.4 lens, not a full stop (i.e., it brings in 1.4x the light, not 2x the light).

For a lot less money, the 50mm f/1.4 lens will be beautiful, sharp, and relatively lightweight. You pay very dearly for that extra half stop of light. Unless you really, really need it, then there's no point in getting it.