You were more correct when you were a "nonbeliever in synthetic." What
you experienced was not "synthetic magic" but a particular motor oil
which had the missing swelling agents to keep your beater's hydraulic
lifters filled. The very same swelling agents might do more harm in a
new engine, swelling the seals to be too tight resulting in premature
wear which then *needs* the swelling agents to work properly.

Mobil-1 is very good stuff, Fly-By-Night Synthetic doesn't deserve to be
mentioned in the same breath. Then again Walmart Supertech oils don't
appear to be the usual fly-by-night junk.

Refined oils are very good these days, probably as good as Mobil-1 was
10 years ago. Experience with synthetic motor oils has taught
manufacturers what works, so today they know better what to make than in
the past. They know what to work toward in their refining processes.

As for the difference between synthetic and refined, its not
automatically better if synthetic. A synthetic motor oil is no better
than the manufacturer cares to make it. There are no independent
performance standards one must meet to sell a "synthetic motor oil"
other than exactly the same as refined oils meet.

There are performance standards that only synthetic motor oils have
passed, but not all synthetic motor oils can pass.

If you are going to drive 10,000 miles between drain intervals then by
all means pay the extra for Mobil-1. But if you drive 5,000 miles or
less in 6 months it makes very little difference. Use an ILSAC GF-4
motor oil every 5k or 6 months, whichever comes first.