From the link:
"On newer water-cooled Porsche engines where Mobil 1 0w40 is recommended, a simple change to an oil with CJ-4 rating or preferably an oil with SL or CI-4 rating as well as a viscosity of 5w40 rather than 0w40 are two changes that can be done in addition to more frequent oil changes to ensure longevity of newer engines."
"Failure to use the right oil, use proper filtration, or observe proper changing intervals can affect the performance of even the best motor oil. It is also worth noting that some manufacturers have gone to shorter intervals and requiring fully synthetic oils (Group 4 or 5) due to litigation surrounding sludge formation and failed engines as a result of factory recommended long drain intervals, so drain interval recommendations are often in a state of flux. Based off of extremely long drain intervals recommended by most European manufacturers, some in excess of 30,000 mi at some point in recent history. Most users have found it best to reduce those intervals by half or even a quarter. Porsche over the last decade has had intervals ranging from 12,000 to 24,000 miles and up to 2 years. Based on UOAs provided to us by our customers, new Porsche owners should consider reducing their drain intervals to no more than six months or 5,000 mi. On newer water cooled models prone to IMS failures, some shops even recommend changing your oil every three months or 3,000 mi allowing for early detection of a failing IMS bearing. Also, remember, Porsche drain intervals are based off a fill of min. 10 quarts, so engines with smaller sumps have to run shorter drain intervals! Cars that have less oil volume can benefit from more frequent oil changes."
Wayne, the owner of this forum and PelicanParts, also recommends changing every 5k miles.
http://www.pelicanparts.com/techarticles/box_oil_change/box_oil_change.htm