I use the Blue box:
http://www.basspro.com/...29-b3cb-00004ef48e51 One thing, and why I mentioned that I do use tippet on the smaller flies. P-Line will be a little bigger diameter than the Fluoro Tippet material.
For me, at 4 lbs and larger it need not be a problem. I agree totally that having the right size (meaning smaller) for small flies will make the fly move more freely triggering more strikes. I like Mirage 6X for my size 32's.
I also think fluoro makes a difference. Maybe just in confidence, but a difference non the less.
I went on a guide get together with five other guides. We all know the waters and fished the same flies. One other guide besides myself, used fluoro. We were catching 3 to their 2. Might be a coincident, confidence, or maybe the fact it really works. But it works for me.
Not saying you need the whole leader as I use furled, just the tippet.
As far as break offs, you can get that with anything. I have had Carp break off 10 lb.
Break offs are suppose to happen, that way we are not running to Cabela's after every outing to exchange a broken rod.
That is also why I like mid flex & full flex rods so much.
Some things are better left alone, Even though, some feel they know better.
http://www.utahflydrifters.com/guides/profiles.htm