Okay so having experimented with Wilbur a bit, I've decided I don't need to put anywhere near as much effort into the individual ridges for the mountain ranges... indeed Wilbur's erosion filter produces far more realistic looking ridges than me anyway! (Surprise!). This is great news, as it means less work to complete the initial Height Map. Still a bit concerned about how Wilbur is going to handle the whole map... :\