I'm gonna weigh in a bit, but not so much on nymphing, but long rods.
I've got three, now. 10' 3wt. 10' 5wt. 11'3" 6wt (switch, so the 3" is all behind the reel handle).
I imagine that all day high sticking the 3wt wouldn't be too hard, and you can do it pretty well with the 5wt, but stepping it up to that 6wt makes it damned uncomfortable.
Its not just the rod weight you've got to take into things, but the weight of the reel you balance it with, and even the line. I took that 6wt out once to a small stream because I wanted length, and my 5wt was out of commission, and it was frankly just too much.
Even just fishing with that 6wt for a day is far more awkward, and tiring, than the 5wt.
I'd spend some time really thinking about the where and how of your fishing, and base it around there. However, if you're getting a middle weight rod, I'd stick to 9' to 10', that last foot the killer.
On the other hand, YMMV. I see your descriptor says "Lehigh Valley." While its not exactly the most opportune time of year, if you want to try and meet up, you can heft all three rods for a little while in some water and see what you think.