Poldo is right, 5 and 9 dont work at all...
For waveriders, the 6 and 9 combo is quite bad too - and most regret and change it, as you got a huge step from 6 to 9m2 - too big
The 9m2 is 50% bigger than the 6m2, and almost double size of a 5m2
You could also get a 5m2 and see how it goes, because, then you can later buy the "perfect" 7 you need most days
Dont know how it works for TT's - but as said, almost everyone here who has taken the 6 - 9 step has regretted it and being a bit pissed most of the times out
So a 5 - 9 is a no go, for sure, unless you plan to buy the "missing link" (7m2) later.
6 - 9 "maybe", and 7 - 9 best choice IMO