Ciaka,
Thank you for the link to the oil article. i have not used AMSOIL yet either, based on my consumption, i will talk to the Indies about it and see what they recommend.
As far as oil change frequency or Service Due indicator to prompt you to change the oil, It depends who is driving the vehicle over time, the Gen 2 CTT i drive tells me almost at exactly 10,100 Miles "Service Due in 1900", its predictable with me and my driving style. My wife in her Gen 1 CTTS currently has a little over 12K miles since her vehicle's last oil change, and no Service Due indicator is yet available. She is not as Boost-Addicted like i am, so her vehicle does not use oil like i do. i think as i mentioned back in April, i use the push-button resettable trip odometer in the dash of both CTT's as my oil usage gauge. When i add a quart of oil based on the dipstick reading (usually at the letter N of the word MIN), i reset the trip odometer and thats my mileage gauge for when to pull the dipstick for a quick oil check (usually between 600 - 900 miles depending on the vehicle and the driver); we engineers are crazy, more like OCD, but for $10-15K for a new engine after failure, i will keep my OCD intact, as it works to my Porsche's advantage.
I also track all maintenance on a spreadsheet, marking oil changes, all oil additions (and a side calculation for each oil addition and mileage between oil add's), and even dealer visits. yes its OCD, but these are Porsche's, its all good. My experience, i can run the castrol to and above 10K miles with no holdback, i could not do that with the Mobil 1 0W40, yes really. i've been using Castrol products for 30 years now, never an issue.
One time, i did take the 08 CTT to 12,800 miles between oil changes, and i noticed a slight drop in performance, i was also at the "Service Due in 200 miles", so the oil was pretty well spent. I was told by a Porsche-Certified Technician at the dealer that the oil level sensor has a heating element in it, it heats up the element, which in turn heats the oil on the face of the element, and based on the response cool-down time at the element face, the oil quality is electronically evaluated, hence giving me typically about 10K miles on normal use of oil life, and then about 2000 Miles to get it changed, as the Service Due counter starts at 2000 miles and works down to zero; basically old oil loses its ability to not only lubricate but to provide cooling capabilities. I like this technology, there is no guesswork, its all smart technology. And i can feel the difference when the oil needs to be changed, its not a monster like it usually is, its holding back, i guess the computers are reducing the full performance parameters to avoid mechanical damage. The Germans know what they are doing most of the time. I still monitor daily the cold-start, and normal temp operation of the vehicle, to see if any patterns develop that need to be addressed, just being an engineer.
I did install Agency Power Diverter Valves in both CTT's, (2 for each vehicle) the Gen 1 gives me better boost, (actually pegs the boost gauge above 0.8 bar), and it flies. definitely worth the upgrade, running stock air filters (i change them every 30K miles myself), CANNOT use a K&N type Oiled cotton fiber filter on Twin Turbo engines, as the oil will get lifted off the filter and will cause the MAF sensor to fail, too much $$$ for new ones. (blogs told me this and it makes sense).
RFM,
5W30 is not listed on Porsche's approved oil list, not for the CTT's or a 911 Turbo, only 0W40, 5W40, or 5W50, all listed in the Owners Manual for each vehicle.
Keep running those Porsche's hard every day, they like it.
Have a great weekend everyone.
Mike.