Re: Reel Sizes
You can do whatever you wish as far as line sizes goes. the 3/4 designation is like the suggested serving picture on the side of the food package. I used an orvis 3/4 Battenkill with a size 5 on it for years and still had about 70 yards of 20# backing there. Before I would spend money on another reel I''d use whatever line I wanted on the reel.
If you are not fishing for big reel stripping fish like I do then backing is not such a big issue. I seldom have trout peel off more than 50 or 60 feet of line on a run.