One board one Sail?

I currently have only wave and freestyle equipment.
I'm running a GPS-Speed contest here in Finland and wouldn't like to be in the last place
I'm thinking of getting one sail and one Slalom/Speed board for the next season.

There are no good speed spots here in Finland. The flatter the water the more gusty the wind will be.
So i will be sailing mainly in choppy conditoins. I would be sailing with these equipment only when the wind is about 10-15m/s (19.4-29.2kn). I would like to be able to jibe the board quite comfortable.
So i'm looking for a fast board with good range.

I will be getting a Starboard board. Would you recomend iSonic or
iSonic speed board.

iSonic 86 Slim 81 243.0 56.5 37.2 6.0 - 4.5-6.5 Drake Slalom Pro 320 24-36 Tuttle
iSonic 86 86 243.0 56.5 37.3 5.95 - 5.0-7.0 Drake Slalom Pro 340 26-38 Tuttle
iSonic 94 94 236.0 60.0 42.3 6.07 5.77 5.2-7.8 Drake Slalom Pro 340 28-40 Tuttle
iSonic 101 101 234.0 63.5 45.3 6.43 6.08 5.5-8.5 Drake Slalom Pro 380 30-44 Tuttle
iSonic 111 111 235.0 68.5 49.9 6.65 TBA 5.8-9.0 Drake Slalom Pro 400 32-48 Tuttle

iSonic Speed Special W44 53 229 44 26.8 4.5 4.0-6.5 20-26 Tuttle
iSonic Speed Special W49 64 230 49 28.7 4.9 5.0-6.8 22-28 Tuttle
iSonic Speed Special W53 74 231 53 32.9 5.3 5.5-7.5 26-32 Tuttle
iSonic Speed Special W58 82 231 58 36.2 5.8 5.8-8.0 28-34 Tuttle

I'm getting MauiSails TR-6 sail but what size? and with what board.
I was thinking something like iSonic 94 with 6.3m2 TR-6 ?

FIN555

My weight is 79kg (174lbs).
Thanks for your input.