I have used it's predecessor, the Selective Trout II, on a true medium action rod. It's a great line, and the LT is supposed to be even better. I would venture to say that on a fast action rod it would still be good for close quarters work and roll casting out to 45'...which is where 90% of us do 90% of our fishing. If I was fishing out farther then that or still waters I would go for the RIO Gold.
FWIW, I plan on purchasing the LT DT in 4wt for small streams and the Gold WF in 5wt for medium to large stream and stillwater.
Nice, in-depth review on the Rio LT... Line review: Rio Trout LT | Michael Gracie
and it's predecessor with a comparison to the Gold... A Fly Line for Trout and for Selective Fly Fishers - Rio Freshwater Selective Trout Fly Line - Epinions.com