RE:Overlining .vs. Underling
Sean, let me try this again... When I first got the fast T&T's, it made sense to overline it to get used to the very fast action. I used a 10 wt intermediate on a 9 wt rod for a while, but soon found I could cast further and easier with a 9 wt line. Only exception was fishing very large flies, where the 10 wt helped get them out further. For a while I used the 10 wt at night, but eventually stopped bothering to change spools.
I just stumbled into a happy underlined setup, but wouldn't think of underlining my 9 weight. The place I fish is very craggy and big bass know all too well how to wrap you around rocks. I've been looking for the heaviest line/rod combo I could 'comfortably' throw, i.e. fish without a sore arm for two hours, which is how long it takes me to fish the place. Throwing big flies is a plus.
I find I just can't use a 12 wt rod/line here, and was very pleased to find that an 11 wt line works well and is much easier to throw. It it plenty heavy to get out the big flies, and the 12 wt rod gives you plenty of lift after a strike. Also, an underlined rod allows you to false-cast more line without 'caving in'. I find I can false cast 60' of line with this without heroics. This is a pretty specialized setup and I'm not really advocating it for all-purpose bass fishing. It's just plain too heavy for general purpose surf/beach fishing. Don't get carried away with this 'recommendation' as it is for a very specific fishing situation.
On the other hand, I do so hope it'll work out for tuna. The ability to get out a fly 80+' with a 12 wt stick has all sorts of possibilitiues...