I currently use a 7.8 and 8.6 Severne Reflex 4 for most slalom competitions.
With the 8,6 having 5 cambers and therefore massive power and at 82kg bodyweight I do use the 8.6 as my biggest slalom sail. The sail planes very early beginning at ~10kts of wind. The advantage of that is that I can take a 80cm wide Slalomboard which is alot faster than a 85cm wide board, I would have to take with a 9.5. The sail is still really fast, but with 5 cams the tuning needs to be perfect for a good camber rotation
The 7,8 and smaller sails have 4 cambers, which is standard in most Slalom sails today. I found the Reflex sails to have great topend speed. With the 7,8 I have done 34 knots in Open Water, with the 8,6 up to 31,5 knots. The rotation on 7,8 and smaller is also great.
Severne’s slalom sails most discussed feature is the Reflex system, meaning that you can put pressure on the battens at about 4/5th of their length, while the back end of the batten is looser. This shall
result more tension in the front of the battens while allowing the back to twist and flex more for more control. I did a little sketch, you can see on the right side. I am trying to get my hands on some smaller Reflex 4’s to test and will give some feddback on the speed-sizes as soon as I get some sessions in.