My commonly carried pistols have 6, 7, 8, 9 or 10-rd magazines. For the one "hi-cap" pistol I own (which uses 12-rd magazines) I also have a good supply of 10-rd magazines for it. (Only 2 rounds difference, anyway.)
Mostly when I travel by car I'm carrying either a 5-shot J-frame and/or a small pistol chambered in 9/.40 that uses 8, 9 or 10 round magazines. I suppose I might sometimes include my LCP with its 6-rd magazines now, too.
Why complicate things?