ORIGINAL: Rob Edwards
Having just made the 'jump' from a 987S (before that a 986S) to a 997S, I have to agree with Mike Butler, and both cars are superb pieces of engineering and design.
However, what sold it to me is the incredible acceleration of the Carrera - it really is on another level to the Boxster - and that is no slouch, I can assure you! The Carrera also enjoys good traction off the line, probably due to the weight of the engine over the driven wheels.
Of course the interior is a little different (obviously more room in the 911 and if you do like to stretch out the 911 is a boon) but I suppose it boils down to whether or not you value handling over sheer pace. I don't think there would be much in at between the two over a twisty circuit!
Rob