Hi JC,
I’ve spent a lot of time on all those boards so may be able to help. I’m also a similar weight to you but much shorter

.
Where are you sailing most and are you planning on keeping the future?
The iSonic 86 (and 86 slim) is more similar in size to the x-fire 90 than the 80. Although the isonic total width is less, the tail is much more square on the iSonic, giving it a lot of power. As such I think the smaller iSonics (of the last few years) are more suited to bigger sailors as it takes more leg strength (and kilos) to hold the rail down once you start to get overpowered. I seem to cruise over the chop much easier on the RRDs, and my legs are much less tired.
So my choice would be: If keeping the futura, get an RRD 80. This board has the ability to go very quick on flat water, but it still has control to be in the rough water in the ocean. I’ve sailed it in 25kt on the ocean comfortably… on my iSonics I wouldn’t have been enjoying it. I’ve hunted a long time to find a slalom board to suit my size for these conditions. This board is the best I’ve found.
It will comfortably take the 6.0, but the 6.7 is getting a bit big for it (ie you would need to be well powered up).
If your selling the futura, and want a board to cover the 6.7 in the lighter winds the RRD 90 might be a better option. It is still a smooth ride in the chop, but will be happy with a 6.0 or 6.7. Depends on where you sail most too. The 90 is more of an all rounder for the river… the 80 might be better for the ocean.
But the best thing is always to try them for yourself. Contact 2ndwind. They have demo’s of the RRD’s and the star board. Or send me a PM. I’ve got one of each board (star 86 for sale and two RRDs) you can try

.
Cheers,
Annika