I use the nine, when I am casting in light wind & surface flies. Either an internediate or the Rio Outbound S-3.
But when the wind kicks up or a heavy sink tip line is required I use the 10wt with a Rio Outbound sink tip. Depending on the depth I want I use a S3, S6 or when one must sink to great depths the S8 line. Lately I have taken to using the S-3 in shallow water as a go to line & change from there as required.