I think #600 is closer to 40-50wt oil, as I saw somewhere that the 60wt is similar to the #900. Problem is that the systems calculate viscocity in a different manner so it is not easy to perform a direct comparison
I think it would be better for all of us if the companies had stuck with one system
When I was looking around the net I found out that even the W with the WT designations vary considerably among different brands..
Given that, you think is better to go with different springs rather changing oil? I know it is easier to change one variable at a time so that we can assess the results better.