Sorry for delay, I was away for a couple of days.
First thing to advise is keep it simple; just as few sails as possible, as these sails all have a very good wide and practical wind range, so with a little fine tuning of both choice (in the retailer and on the beach) and then fine tuning on the rigging itself, you can have a really good range with minimal equipment, which has a lot of benefits.
One factor I would also consider is the 6.9m Jet, which (with all respect to NP etc) did not show itself to be an ideal sail for use in heavily powered or loaded situations (as it was a relatively lightweight "sport" sail without a lot of draft stability - something a 100kg rider usually needs lots of !)
So I would be wondering 2 things before deciding : 1) is the 9.5 C2 you're using getting a lot of use - and in ideal 9,5 conditions (or are you mainly using 9.5 in "8.5" conditions ?? - and 2 ) what about considering something a little bigger - but more stable- to fill out the quiver from the bottom(6.9m) up - say, adding in a more stable 7.5m , for example, which could help close the gap to 9.5 from the bottom up, rather than dragging 9.5m (if you use it a lot) down.
in general, while having 3 sails to cover the range of 9.5/8.5/7-7.5m would be nice, it's not really essential, and you should be able to do it reasonably well with 2 - if they are not too far apart.
Hope this helps you in the decision making. Let us know if you would like more info etc.
Cheers ~ Ian