DUDE , I am same weight and although my biggest sail is a 9.0 RS/6 , I am having a quiver of an 80cm (falcon 131) and 62cm (exo TBII) wide slalomboards.
I have sailed the 80 wide many many times this year - using racing sails from 9.0 / 7.8 even to 6.7 with only changing fins.....my 62 wide I used most of the times with the 6.7 but also a couple of times with a 5.8 m2.....
This set has given me so much options and doubled my TOW , just change fins and keep flying !!! Some friends are sailing Starboard Isonics in similar boardwidths and all have mentioned that with 85-90 kg riderweight this is by far the best combo to go with.
I have even been GPS racing with the 5.8 and 27 lessaccher speedfin and had a briilliant time with it....
Good luck with choosing the right boards