I'm in the learning phase of Spey Casting and have had no formal training, only the one-on-one help of some very accomplished casters.
Now that I have made my disclosure statement, I'll try to help where I can untill someone wiser comes to the rescue.

From the information I recieved while trying to select a line for my rods, if you are a novice caster, the Windcutter in the 10-11-12 would be the right choice. As for the Grand Spey, the line is geared towards more experianced casters, i.e. not me. I have heard some good reports on the XLT, but have personally only cast the Windcutter and Mid-Spey. I would suggest posting this same post on http://www.flyfishingforum.com/
Go to the link for Flytalk, and scroll down to the Spey Clave section. there you can read posts on lines as well as do a search for the info. If you don't see what you're after, then I would leave a post asking for the info. There's a world of info out there, just gotta' look!