I visited a local gas station and lifted up their latest SPC 0w30 oil to have a look. Boy it felt so much heavier than the Castrol SLX I had bought. After checking the SPC specs , I found out it indeed had a much higher SG compared to Castrol SLX specs . Is higher SG better or lower SG better?
0.868 specific gravity is not that unusual. Most dinos have similar and higher specific gravity. However, most synthetics have lower specific gravity. If the SLX you have is the same oil as the German Castrol, it has the lowest specific gravity I have seen in an XW-30 (~0.843). I think that higher specific gravity is one aspect of an oil that helps to reduce oil consumption.
All that said, the difference between the two is only a fraction of a pound per gallon. It does not seem that it would be easy to tell by hefting it.