I think the 6'1 would be a great step coming down from a 6'9 and you will definitely feel how much better it is to pump around and link bumps. At 65kg you will have no worries on the 85L, i am 77kg and can ride it no worries.
At 73kg I started on a Takuma ZK 6'10 x 26 - 100L, then custom 5'10 x 26 - 110L, custom 5'9 x 26 - 100L and my next board is 5'5 x 26 - 100L.
I think having some volume hepls with stability and the buancy (especially thick rail with concave deck) helps in big ocean dw conditions (side chops, moving water, etc...).
The shorter the better but you still need to be comfortable enought to be able to paddle hard (at least 5 or 6 powerfull strokes to get up and fly).