RE: Old Race Sails V's New Race Sails
Sails have changed significantly since 1996.
Your Gaastra F1 probably was designed and made a little before the discovery of the advantages of "top twist.
I suspect, since you are planing so well and so early on the HS 96 that your F1 is a very powerful sail, and has a very deep draft (by todays standards).
So, I think you will be able to get quite a bit more top end speed out of our Hypersonic with a modern "twisty at the top" rig. It will certainly handle the gusts better than your F1, size for size, but I think to get the same results, and better top speed, you will need to make your current design rig about 0.5-10 m2 larger.
For the Hypersonic 96, an 8.5 m2 rig is about as big as I would go, but the board really gets awesome with about a 6.6-7.2 m2 rig in about 18 knots of wind.
Many will tell you that race sails are better, and I would agree if you are talking "slalom race sails" in the 6.5-8.5 m2 range, and most of the current "slalom race sails are 3 or 4 cams in this size range.
So, either a free race or a slalom race tpe sail will be good, you just need to decide if you want to go after every last bit of top end available with the Hyper 96, or just sail as fast as possible with something a little less complicated and lighter in weight (a camless free race design).
Hope this helps,