Generally this thread has the SL beating the SLR. How ironic.
As for my experience: I went from Classic Mojo (ordered before they were in production and waited many months, maybe 10?, for delivery) to the SLR (ordered when I thought they were in production but still waited 10 months for delivery). The SLR is much stiffer and overall a better ride because of that.
As for the SL, I haven't ridden it. While it was a bit lighter than the Classic I was never convinced it was stiffer or in any other way significantly better so I never thought it added much advantage besides some ounces. With the SLR I was promised weight loss AND stiffness. Well, I got loads of stiffness but not as much weight loss as promised.
So, IF it's true that the the SL is very stiff compared to the Classic, then it's a great deal because it is stiff and light and easier to obtain and equip than the SLR. However, if the SLR (with tapered headtube and carbon weave improvements) is stiffer than the SL, it's up to you to decide.