I wouldn't call higher gas mileage a performance gain....but I have heard many people claim that since the synths are slicker than natural oils they tend to lead to higher gas mileage....whether you believe it or not, I didn't get any higher gas mileage, so I don't believe it.
For weights, it's unfortunate Mobil1 isn't made in 5W20, right now I have 10W30 but need to bump down to 5W30.
Thinking of which....I need to change my oil.
b