Can't believe I never knew about this site until now! I'm an enthusiast who's been using Mobil 1 since 1986. Also during that time I've had a couple of turbo powered cars. In those I always use Redline because I believe it offers a higher degree of protection than any other synthetic that's easily available to me. I always used 10w30 Redline based on my converstion with Roy Howell of Redline some years ago when I had my S4. I now have a WRX and I just switched from the 10w30 to 10w40 for the summer months. Interesting that the 10w40 looks (darker) and smells different than the 10w30. Anyone know if the additive package is that much different between the two? I think I'm going to love this site!