I can echo (sort of) what Adam D and Dreamer have said above about Boxters/Caymans.
I had an hour to kill before taking the Z for a service and thought it would be a jolly wheeze to have a sit in a late 2009 Cayman at a nearby Porsche dealer. I made what I can now only reflect on as the grave error of allowing the admittedly polite and attentive salesman to force me into driving the bloody thing.
This Cayman had 19' wheels :| , sports exhaust

, short shifter

, active suspension

and LSD (not tested). I got a good drive up and down the same excellent part of the A6 I had punted the Z down about 15 minuts earlier.
Staggering steering feel, precision and turn-in, pancake-flat cornering (especially with the active suspension switched on), lovely short-shift gear change with a precise and direct clutch, exceptional poise, balance and ability to change direction quickly. Didn't really test the brakes properly (with all I've said before there wasn't any need to shed much speed for the bends) but they are not as heavily servoed as on the Z.
I love the Z in general and my M in particular. But the Cayman is a scalpel to the M's bludgeon.
In terms of the overall drive, I though the Cayman was the best car I have ever driven and I now can't get it out of my head. But the cost to change is slightly more than I paid for my pristine, well-specified 9 month old Z when I bought it 2 years ago and that just seems wrong. Plus having cleaned and waxed the M over the weekend, I still think it's the better looking car.
The tales of reliability problems and big bills will, I hope, help me to overcome my latest obsession.