F-69;
MAYBE, (only guessing here?), that whoever is building your rod, is also trying to sell you a reel?
Anyway, I've fished a Battenkill M/A III all winter, this past season, and taken my largest metalhead of 14 poundsf (for 2007), on it and it didn't even break a sweat.
It also, brought 11 other steels to the net, all well over 6 pounds with no problems.
Of course, I don't know about the steelies in YOUR immediate area, but ours when we're lucky enough to connect with one, have JUST come in from the sea and are none too happy about "being bothered by a scroungy looking steelheader" so they "fight and run", extremely hard and long most of the time. "Enough backing" is of a real concern on some of our larger, steelhead/coastal rivers here.
The current of our rivers, is also quite heavy and strong, (adding to the fish's fight and the wear and tear on a drag), because they fall from the coast mountains, in a fairly short distance, to the ocean. So, the two things added together, can make for some "interesting fishing" to say the least!
But, my Orvis BK/MA III, loaded with a WF/6/F and 100 yards of backing, still has a full 1/2" of room before the spool would be considered "full up".
I can't see any problem with you having a 100 yards of backing as well as a 7wt. line on one, without crowding things at all!?!
I'd also, check with a fly shop that peddles the reel, and fills them on a regular basis if possible. They should be able to tell you, if your particular line will fit properly or not, with the amount of backing you prefer. And also call and talk to an Orvis employee and ask THEM, what they recommend for your set up!
Saint Paul-"The Highly Confused"
You cannot do a kindness too soon, for you never know how soon it will be too late.
-- Ralph Waldo Emerson