My current mileage throughout the last 4 months has been around 10 miles per week running and 30 on the bike. My swimming has been a bit less intense as I have a sprint triathlon approaching which demands more from my cycle and running. With the swim being complete in around 8mins for myself, the better swimmers will only be making around 3 mins advantage in the pool, which can be made up easier in the cycle and run.
So, as you can see, my starting point for IronMan 2013 is that of a distinctively average fitness level and ability. But like I say this is a starting point!