I do the same as Keith for outdoors. Pro 160S at EI 125. You get a bit of extra latitude over the C. The C has slightly more vibrant colors, but the S looks very natural, with great differentiation of subtle color variations, and I like the extra latitude for landscapes. In really flat light or low contrast, or if I wanted to punch up the colors, I might go for the C. But 160S isn't a compromise on color for me. I tried both and then ordered a large batch of the S.
It's a little bit along the lines of S = Eliot Porter and C = Pete Turner, but more subtle a difference than that suggests.
Lee