Re: Rio LT fly lines....
I have been fishing the Selective Trout/LT on a TXL since I picked it up a couple of years ago. I did some research and found that many folks recommended pairing the rod with that line. I don't regret the decision, seems to be a very good match. That rod was rated as Medium Fast by Sage. Depending on your stroke preference and rod manufacturer preference, your opinion on Medium Fast may vary. Have also fished the LT on medium action rods and found it to be equally solid.
Which fast action rod are you considering pairing it with? I might be inclined to think Gold may be a better match for a fast action rod, at least from my experiences. Spool it up and throw some line with the fast action and see what you think.
~*~Leave only your footprints~*~