Speaking of Oil again.

What are the differences (benefits) do the "high-mileage" or "extended use" or "clean 7500" type oils have over the standard oil?

They have additives that are supposed to help them work better in higher mileage engines, something to prevent oil that gets past the rings from smoking and something to keep gaskets softer and pliable so oil doesnt leak. You can get the same thing I would think by buy buying cheap oil and adding a good oil additive to it at oil changes

I think that from what you've said the additives in these types of oil should also be applicable to newer engines since what they do as claimed are preventative measures other than corrective. By this I meant that when an engine is burning oil, this type oils will not fix it. I read an article in the API (American Petroleum Industry) website stating to the effect that some oil additives sold separately chemically conflict with the additives already in the oil. My reason for pointing this out is because when one goes to buy oil, there seemed to be so many oils now its confusing. Many believe that the more the oil cost, the better. I for one is sticking by the car manufacturer's recommendation in the User's Manual.

I still use the cheapest oil on sale and an inexpensive name brand filter and change my oil every 3000k. I have yet to have an oil related engine failure in any car ive ever owned

Toddler62. I'm with you. I have a 99 Ranger 4.0L and an 2000 Acura 3.2 TL and I've been using the standard brand oil 5W-30 and the standard brand oil filter. I also change oil and filter in accordance with the manufacturer's instruction. The only additive I use is a fuel injector cleaner which I add to my gas at oil change intervals.