Depends on the driving type and weather. I have a 2000 Jetta diesel with 334,000 miles and I change every 5,000. I work on TDI's and have noticed a difference with cam's in cars with 10k changes. If u look at my cam you can still see the mill marks with a little shine around the tip of the lobe. On cars with 10k changes you can see wear marks.
Of course, then you can get into the brand of oil. At the TDI club there was wars about once a month on "what is the best oil" lmao.
Now, when I was younger the rule of thumb was change the oil as soon as it starts to darken up. But that was dino oil not synth.
regardless, on a gasser I would assume 10k would be the rule of thumb but again it would depend on the driving type. I might even think you could get 15k-20k if driving nothing but hi-way on a newer engine (less then 100k). You can buy kits for oil testing too. I think it is around $20. you take an oil sample when changed and send it in and they send you results via snail mail.
wait a minute, your name is fatboyracing, shouldn't you know this? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif or do you race fat boys //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif