I'm not a fan of overweight lines but I use a Rio Smallmouth line on my 6wt outfit which is a 9'0" Winston BIImx, a rather fast rod. All I do is pick-up, make one or two false casts until I'm at the spot where the line changes color and I let it fly...
I did a lot of research and chose this line based on conversations I had with folks at Rio & Sci Angler about my rod's flex, my style of fishing and the flies I planned on casting.
If nothing else, if I was buying another line for a different rod I'd approach it the same way and make a few phone calls and ask questions...