Huh! My (UK) CRDi Comfort auto is on 16" Hankook K415's, just had to replace a rear tyre today at 4000 miles as it had a screw through the shoulder, so yours have lasted better than one of mine!
Good to hear that your fronts have lasted 16k - I suppose in that case I may have a complete set of Michelins in a years time! I think that if the rears were likely to last 40,000 miles I would be inclined to put them onto the front so as to wear them out before they get old.
My experience of the Hankook K415's is that they hang on well, but I think they seem noisy (ie road noises). I will be interested to find out whether Michelins (Energy Savers) are quieter than the Hankooks, and hang on better or at least as well. I might have preferred a Continental but didnt have the choice at my local tyre dealer when I needed the tyre - one of the drawbacks of not having a proper spare wheel.