just looking over the prices on the bay... the price is pretty much the same for 350 or 500mm... seeing as there is a considerable difference in the focal length, would it be a safer option just to jump straight on the 500mm? It is a pretty big lens though!

also, I'm assuming that with a 350mm and longer you're going to need to have the tripod mounted on the lens rather than the body, how does the camera/lens hold up with that weight where they join? has it been known to damage the locking mechanism at all?