RE: Pros and cons of smaller sails on Formula
If you want to maximize your TOW as suggested by Barks above, I also recommend to get a 11 m2 sail to be a perfect match with your new Formula board in low wind (do it later, it looks like you're not ready yet, however).
When I added a 10.6 race sail in my quiver about 7 years ago, my TOW simply doubled (yes, 2x more TOW than that combined with all the remaining 9 sails) because the numerous light wind days at 7-10 knots were finally much much more enjoyable at full planing speed as compared to the boring schlogging TOW I had previously with the largest 8.2 sail at that time in such low wind. When I consider the TOW/$ ratio for these 7 years, no question it has been an unbeatable bargain and I've ordered a new 11 m2 sail as a much needed replacement. I bet sooner or later you'll be lurking at a larger sail to increase valuable TOW in low wind...
PS : don't be afraid of the "giant" leap between 8.5 and 11 m2. In low wind, it's not uncommon to have 2-2.5 m2 surface difference (constant wind range for my 65 kg : 7-12 knots with 10.6 m2; 10-15 knots with 8.2 m2).