I only have the 2 1/2 strip cutter. I usually do my bindings with 2 1/4 and that was the closest one..I can just sew a little bigger seam allowance. Rarely do I use the other size strips so I don't have those.
I wasn't aware of a 3.5 or 6.5 strip cutter. I only have the squares and 3.5x6.5 rectangles. Strips would be nice for borders.