I struggled with the same question. I ended up with the poly sleeves with the "fold-over" tab made by Pro Line. I use the "unperforated" roll, which I cut into 6 1/8" lengths. I cut my negatives into strips of 2 (5 per 120 roll). Although not as handy for printing bunches of negatives, it works quite well when working with one image. I don't proof "pages", but instead print 4x5 "proofs". I don't spend any time fiddling with exposure as I always do them the same. Enlarger height to just cover a 4x5 sheet of paper, f16 & 8 seconds works for me. Doing them the same also lets me see if a negative is grossly over or under exposed. I write a date code and frame number on each of these prints, and keep them in a file. If a family member wants one, I have taught them that they only need to write the number down *Never* taking one of my proofs. Which in itself isn't a big deal, but if I make them think it is then I never have to sort back thru the negatives to see which one someone took. Having the date code written on the border sort of helps to deter them also.
Reading back thru this makes me wonder if I am having a hangup with quote signs today.
I was using Printfile 120-3HB for my 6x6 negs, but they hold 9 (3 strips of 3)negs of the 6x7 size. PITA when you shoot 10 on a roll. I have sinced switched to Printfile 120-4B that holds 8 6x7 negs.(4 strips of 2) At least this way I don't need to worry about single negs. One roll of ten takes 2 sheets but at least the negs are kept in pairs. Print file also makes a sheet that holds 9 individual (not 3 strips of 3 or 4 strips of 2).
I use Clear-File 120 format sheets. They are designed to hold four strips of negatives. I get ten frames per roll with 6x7, so I usually have two strips of two negs, and two strips with three negs. I like to have min. two negs per strip for enlarging. Easier to get into the negative carrier. Then each roll has it's own sheet, and they are stored in an archival box with rings.
I couldn't figure how they would squeeze more space out of the 8.5"x11" page but you reminded me that they often use those extended sizes for things like 7 strips of 6 35mm frames.
That 4 rows of 3 6x7s solves my problem.
That is called grain. It is supposed to be there.