I've been putting Mobil1 5W-50 in my 505 turbo for about three years now and
I couldn't notice any improvement in running smoothness, gas economy, and
all other immediate benefits other people claim to have seen. It appears,
however, that long-term benefits like reduced wear are for real, and this is
why I keep on spending money on Mobil1.
Just my 2 cents,
Radu