I would say that Dragonsfoot would be a good place to go for Myth/Hist style questions, since their specific-edition focus will not be a hindrance there. Otherwise, I only really know sites dedicated to various game systems or settings (such as the Piaza for the D&D setting Mystara/Known World, or Citizens of the Imperium which is the main Traveller site), are fairly political (RPG.Net or therpgsite), or constrain allowed topics as a reaction to politics (here, RPGRpub, enworld).