The new features in 374 have yet to be used by any mods (I think), so bugs in the new code won't manifest themselves.
Also, the "official release" version of Forge has bugs on its own. Forge 372 (and earlier) has a bug that was fixed in 375, and another that was fixed in 379, and another fixed in 380.
As for which version Optifine requires, that's a question for sp614x. I, personally, haven't had any problems installing Optfine on versions of Forge that it wasn't specifically intended for, but maybe I've just gotten lucky.