my buddy works for MBZ, I get free Mobil 1 5-30 Synth Oil. Been using it for the past year = 20k. No sweat. If anything, my car runs better with the synth, unless I'm going crazy. It also no longer idles as rough as it did when I was using organic oil. Overall, no change in fuel economy, but then again, driving your scoobie hard, as I do, will lead to some pretty pathetic gas mileage, ~15-19 mpg. Bottom line, if it's good enough for CL600's, S600's and the whole AMG lineup, my $24,499 WRX 'Rally bred' tough as nails motor, should be just fine. BTW, no need to change your synth oil any earlier than 5k, unless you drive less than that in 3 months. Also, if so many of you are worried about how to prolong the life of your motors, try not abusing it, AKA beating on it without mercy at the track/street. Otherwise, know that the car will not last an infinity. In the end, unless your negligent with Oil changes, your driving habits will have more of an impact than what weight/type of oil you use. Lastly, the most traumatic moments of your cars/motors life are at startup, and stop, while still hot. So take it easy the first and last 10min or so that your driving your Subie.