If you're at 75 kg now, the EVO 70 is a given in a two board quiver. It will be a fantastically all round board for you. The Question is then EVO 80 or 90 for the big board. The 80 can handle 6.0 and feel nicer when powered up than the 90. But the 90 will be mroe relaxed in underpowered sailing and a bit more effective with a 6.0.
I'm around 70kg and for me the 80 is a big enough big board. I've had the 90 some seasons, but it just didn't offer much extra for me. But the 5 kg more may make the 90 a more valid option.
But I think you should try out the 80 on a 5.7 day first and then decide.