According to the specs the Long delta is 61.5' and 550 grains. Midspey 7/8 is 65' and 560 grains. Long delta averages 8.93 grains/foot for the head, midspey is 8.6. Midspey 6/7 is a 57' head and weighs 490 grains. That works out to 8.6 grains/foot.
I cast all three lines on the T&T several different times in consecutive rotation. If you want to feel the difference cast the Airflo first then the midspey 7/8 and finally the midspey 6/7. You will see what I mean about the rod losing its action.
Yes the rod will handle any of the lines (it will probably even handle a midspey 9/10 if you forced the issue). But I feel it comes with a price as it becomes more work to make a consistant, pretty, cast with the midspey 7/8 and long delta 6/7.
A guy asks a question and he can get a range of answers from great casters to complete neophytes. That is the beauty of the public board, how do you sort through all of it??? I just gave the results of my experience with the different lines, now it is up to squach to sort through the BS, spend some dough on a best guess, and hope it is not a mistake.
So with that, the BEST advice is to go down to the local shop and get ahold of demo lines to find out which one works best for your ability and casting style.