Not to be a stickler, but 6 quarts sounds like overfilling to me. The VW dealership I used to have my (don't have it anymore) 04 GTI serviced at routinely added too much oil. So, now I do it @ my local garage..
my manual says 6 quarts. with filter change.
sometimes without filter change manuals will say almost a quart less.
more oil, if it has a pan to handle it. plus whats runngi in thelines for hte turbo. more fluid longer to get fully dirty, (might be kinda why the manual says 5000 miles for change) and longer to heat up. maybee.
if you look at soem dealers like ford with a service plan. service plan for my dads truck is every 5000 miles. for his buddy wth no service contract its every 3000 miles. and they said it was becasue m dad had the free service plan it was longer
And i think someone said they emailed mazda about synthetic oil. and mazda does nto recomend. probably cause they havent tried it. but they dont!