Thanks for the advice.
I was only going to buy the select sl07 37cm for my 7,3 sail but there was a 50% discount on maui fins sl from 2007 so i figured i could extend the board high wind range with a smaller fin for use with 5,8 sail unfortunately there was no 30cm fin and i tought that 32cm was a bit to close to the 34 that i have(looking back the 32 would have been the best choice). I was not fully aware that wider boards require bigger fins. Because I only have one slalom board I have to try and make it work in as wide range as possible. If we get 30knots of wind I will give it a try and if it does not work I can keep it untill I get a smaller board. I will try to get back with my impression, might be a while untill I get the conditions for it tough.