997's also have no ABS, so that can be a bit of a leveller in some conditions and tracks. Running cost comparisons working in the 997's favour could also be very much related to the use the car has had also.
I was contemplating a cup car last year, and thye huge expense that the 180 had taken to get where it was and the cost of all these 996's really got me thinking and it's what prompted me to really start considering selling up and moving on. In the end my decision came down to the SR3 or a 996 Cup Car and I went the SR3 for a number of reasons, but first and foremost was fear of the running costs. I had a good idea of what engine and 'box rebuilds were worth and they were a hell of a lot higher than what I'd be up for in a 996, and the Radical is quicker on most tracks.
Having said that, the person I bought my Race Ramps off runs Cup Cars and was convinced his running costs would be less than mine so I'll have to catch up with him at one of the rounds and compare notes. GMR look after a Cup Car and speaking with the guys I'm thinking my car is the cheaper car to run, especially if you do some damage to the bodywork.
I'll still get a Porka one day though, but it will most likely be a road car or a classic 911S/356 etc