I e-mailed Castrol in Germany last night and requested the data sheets for the Formula RS 0w40 and 10w60, as well as the TWS 10w60. The sheets they sent me are all in German, but here's the relevant data on the 0w40. I'll post the 10w60 specs later. (The Formula RS 10w60 and the TWS Motorsport 10w60 don't appear to be the same oils.) Castrol Formula RS 0w40 Pour Point: -61*C Falshpoint: 236*C Viscosity @ 40*C: 75.2 Viscosity @ 100*C: 12.9 Cold Cranking Vis @ -30*C: 3250 Viscosity Index: 173 TBN: 11.1 A couple of things jump out at me. First, this oil is formulated on the low, low side of the 40wt range. At 12.9, it's barely a 40wt. Second, the VI is actually lower than the SLX 0w30. This tells me the viscosity spread is accomplished almost exclusively with the high VI base oil blend.