Well, what i know is that if your motor is overhauled, I mean change of parts just as a new engine, then a full syn motor oil will be good. Example: a new car can always use full syn from day 1 and won't suffer oil loss. I had been using Mobil 1 Full Syn since 3 years ago (on new car) change oil every 12000-15000 km, no problem, no lessen oil level, and I travel at high speed a lot, in highway usually at 160-180kmh. Car is a Elantra 1.8 auto. My mileage now is nearly 100k already.
Thanks