I don't think a 122 with your 7.5 will be worth the investment. It would make Starboard happy, but the gain in early planing will be negligible. On the other hand, the slogging will be more comfortable.
The decision on going larger pretty much depends on how many more days you could get per year with a new board and sail. If you sit home 10-20 days a year because the wind is 14 - 17 mph, then bigger gear may be worth it. I am guessing that with good pumping, you could get the futura 141 with an 8.5 planing in 12-14 mph winds (maybe with the 133 if you pump your brains out). If your wind is usually highly variable (8-17 mph for example), staying on plane will be impossible in those conditions (less justification to go with the larger gear).
If you go up in sail size, one meter is a good jump in this range, so I would go with an 8.5,but only if you go for the 133 or 141.
When you jump up in sail size, it's normal to feel overwhelmed with the "giant" sail. If you stick with it, you will become comfortable very quickly.
In my early years, I was always enthusiastic about going up in sail size, thinking I would be planing and smoking across the water at great speeds. I was frequently disappointed with the gain in early planing and speed, just to keep things in prespecitve.
I agree with Roger regarding a 9.5 (or 9.0) sail. If you go that big, you should go with a larger board (150) to better cover your low wind range (12-17 mph).
I guess your goal is to cover the broadest wind range with the least amount of equipment. We all have gone through this dilemma. Some of us go for maximum coverage (my sails range from 4.0 - 11.0), but many others choose to go with only small gear (4 - 6.5/7.5) and only go out when the wind is 17 - 35 mph.
What do you do when the wind picks up? You may have to consider going down in sail size too, since a 6.5 will be a bit large when wind approaches 25+ mph.