6, 9, 13 (even 14m) also a go-er for ultimate range.

You have to accept that you will only use the 6m in winter and the few
really crankin days in summer.
Also that the 14/13m will not be anywhere near as fun to ride as your 9m but way more fun than chilling your date on the cold sand.
Having said that I ride 7, 9 and 12 but kinda wish I had a 13m or 14m for genuine low wind. My 7 really is more like a 6 and funnily my 9 more like a 10 tho.

Have I confused you yet?
Look for bargains in the big n small kites but spend on your middle kite (if it needs replacing down the treack) as that is the one you will be on most of the time.