On a more serious note, this should give you more insight and is fairly easy to read.

http://www.amsoil.com/lit/g1490.pdf

 

Yeah...it's about time you showed up

 

Why not do like this dude, Lobuxracer doing, have the oil analyzed. The Lab even willing to send the kit to you for free!

Facts trump over-killed-paranoid opinions!

 

Mobil 1 synthetic, changed every 5k as I run my car pretty hard. I'm gonna switch over to amsoil next since I hear such good things about it.

 

really dont matter how hard you run the car. a basic oil change is recommended every 3K. semi Synthetic is 5k and a full synthetic is 7k

so for example Castrol GTX 5w30 should only be ran no moer than 3k

 

It's impossible to say what the correct interval is if you don't analyze the used oil. If you use the recommended interval, you won't go wrong unless you drive very short distances and never get the oil to temperature (3 bars on the oil temp gauge), if this is typical for you then you might need shorter than 5k changes.

So, the easy thing to do is change it at the recommended intervals (5k). I consider all the risks, and have my oil analyzed so I know with great certainty what is reasonable for my driving patterns. As always, YMMV depending on how you use the car.