This is probably one of the best lines for a switch rod on the market. http://www.beulahflyrods.com/elixir_flyrods.html
My question is what are you trying to accomplish though? By this I mean are you looking to stick with spey casting, or do you want the rod to be able to do both overhand and spey casting. Also remember the 3- 3.5 times rule for head length. It still applies to switch rods, that is if you want to stick to some spey casting.
I myself fish several lines on my switch the 8wt. Sage Z-axis.
Rio Skagit 400gr. with 13ft sink tips at 129gr.
Rio Outbound at 425 gr. which is a 10wt. line
Exlixir at 420gr.
I think you are really going to have to overline that rod too. I played around with it at a spey clave this past fall and had a very difficult time getting the rod to respond. The funny thing was even the rep. had difficulty with the rod, which is not good. I would say that if you are going to be sticking with a traditional line look at least 2 line wt. heavier for that rod.
-Mike