Cloud,
Run the car with a little bit more oil than shown on the dipstick as full - no problems. I have not run slicks, but R-Spec tyres and have never had a problem. This was one of the first recommendations that my mechanic in QLD told me (and also the mechanic here in WA that has a lot of experience with the 944/968's).
For the Cayman/Boxster, you can buy a larger sump pan that gives more oil and a deeper bath. One of the Guy's (well his name is Guy as well), has a turbo Cayman with extended guards, etc. he runs the bigger sump, plus an accusump just to make sure on the engine side.
The standard 3.4/3.6 engine in the 996 and Series 1 997, does not like track work. There are lots of threads on the problems with this engine (which can all be fixed, for a price). 996 series 911's, particularly the early cars, are now very cheap, even here. The price is now down around impact bumper 911's and getting close to 968's. if you trash the engine, it is a $20k new purchase from Porsche, or roughly the same to have it out and do the mods available (sleeves, etc). But if you mod your engine, you can stroke and bore it to a 4.0litre version.
So while tempting, it could be very painful.