Alex - good idea to try and quantify the models etc.
There are now 2 * 3.6/3.8's (same crank), 2 * Cayman S's (one a race car), 2 * 3.4 996's and 1 Boxster s 3.2 (so 7 all together covering 3 crankshaft types).
You could generalise that although there are exceptions - they seem to last between 80 and 160K in road use and 500 to 1K racing miles (although for racing several engines are running with sump extensions that do not prevent oil evacuating the sump in corners when using slick tyres and these last the least while engines with reliable racing sumps and ACUsump safeguards seem to last nearer the full season (around 1K) but upon stripping for a winter rebuild have worn shells that need replacing.
Baz