my words on this thread

i have a different schedule  for my cars depending on pattern of usage.
I believe the the frequency/brand oil is much less impt than your
driving habits in determining bottom end life of an engine.

1990 Audi 80 driven 400 miles/week on highway
	change oil and filter every 5000 miles or as climate
requires (upstate NY varies between 100F and -25F in a bad year ....)

1983 Quantum driven 10,000 miles annually - two oil changes a year as
required by seasons

1983 diesel Vanagon - about 10,000 miles annually - two oil changes and
one filter change every year - this one is really unhappy with 20W-590
oops  read 20W-50) at 0 F.   

I used to change the Quantum's oil every 2.5K - I bought this at 60K and at 
120K it needed a ring job in the worst way - which i blame ont he previous
owner without shame. 

None of the above use any oil in the 5000 mile intervals - i even had the oil
analysed once by a bud in the fleet business and 2.5K oil and 5K oil 
spec'd out identically.

do what makes you happy imho

use castrol and OEM filters exclusively btw