The fly line standards that we are using today were developed back in the split bamboo era and are out dated for modern graphite rods, especially the fast action rods. I had been using SA Titan lines on all my streamer fact action rods and really like them. As Rob said, they are 2 weights heavier than the designated AFTMA line weight. So in this case, just match your fast action rod weight to the SA Titan line weight and you are set- 6wt rod to 6wt SA Titan line. SA also just came out with a new Titan Long which has longer handling section than the regular Titan. If you are the type of caster that like to carry a lot of line in the air, the Titan Long may be the line for you. The longer handling section also give you better line control in the water, mending.