Don't know what this means, but when I used Castrol GTX I noticed that it got dark faster than when I used regular Mobil. It was the same when I tried out both of their synthetic lines. I think it has something to do with being able to suspend more contaminants and or for a longer period of time. I've never tried Valvoline but imagine it would be one of better conventional oils out there.
This may be silly but do you guys go around sniffing the new oils that they get to compare with another brand. I've noticed that some smell more like burning oil while other just don't really have a smell. I just remembered...I live in Houston and was driving past an oil/gas refinery and it smelled exactly like the bottle of Shell oil that I used in my sister's car. Hahaha.... I think this oficially makes me a car nut. Literally...
