Mark,
I must caution you to be careful with uplining a rod simply because some folks don't like the way it feels with the line it was designed to cast. Remember, just like with single-hand rods, different folks like different actions and amounts of bend in the rod when they cast. Folks who like to feel the rod bend down into the cork on nearly any cast often upline as much as 2 line sizes with the moderately fast recovering, moderately stiff rods like the Forecast spey blanks to make the blank bend to the cork on every casts. However, just because they do so, doesn't mean you should.
I like fast recovering, stiff, with a strong tip 2-handers like the T&T, Mesier Highlander series (personal favorites), Carron, G. Loomis Greased Line series, and Loop Greens. As a result for me, the Forecast blanks feel best when lined with the blank's rated line in a short to mid-belly line. I don't like them with long-belly lines because I don't like the way their less strong and stiff tip feels with a long-belly.
Another example of this is the old Sage 9140-4 (14' 9/10) "brownie", which was my first 2-hander back in 1992 or 1993. There are many folk who loved and many who still love this rod; but I hated it because it bent so far into the cork and had such a soft tip and blank. I fished it for 3 years before I wised up and went looking for a fast, stiff rod. Even with a 7/8/9 Windcutter line, the rod was still way to slow for me, and that was with a line 2 sized lower than it was rated for. But at the same time, I knew 2 people who like it best (one still used the rod a lot) with 10/11/12 Windcutters, which are a line size higher than it was rated for because they wanted it to bend even more.
What I'm trying to convey is that the only way for you to really know which line will work best for you is to cast it with 3 different line sizes. You can make a very good educated guess that will probably be a decent match for you if you keep in mind the type of rod action you like and then either use the Forecast recommended line size, upline one size, or upline two sizes. This will at least get you very close and not be a shot in the dark based upon what some other person prefers in the way a rod bends when casting without providing you with the information on the type of rod action he likes (which is why I provided you with the type of rod action I like and some examples)