Maybe worth mentioning track insurance at this point too. It's far from a must-have, and it's not exactly cheap unless your insurer can add it to your policy, but it's something that I would no longer consider an option personally. It's not my driving I'm worried about, it's someone else being an idiot or having a mechanical failure (like the poor chap had on here recently that ended up with him writing his car off) that puts you into a barrier at speed.
I don't have track cover for the MX5 as its only worth about £7.50, but no way I'd track the 911 without it. If you've got a nice slush fund then maybe not worth it, but if not then ask yourself if you're happy taking the risk. All that said, I've never personally witnessed a car to car incident at a TD, and only a handful of car to scenery ones, so they are rare but it's worth thinking about IMHO.