2.6 should be a 2.6 mm stitch. There are 25.4 mm per inch so that is just under 10 stitches per inch. The setting of 3 would only be 8 spi.
I am different than most of you. I use a 2.0 mm stitch (~ 12 to 13 spi) for piecing and 2.5 (10 spi) for binding. I definitely wouldn't use an 8 spi.