AL Merrick skinnyfish

[morph]

so i've a 7s fish thing i bought in portugal after my boards got nicked of my car (gutted). I got it cos it was cheep, turned out to be a great fun board especially in small waves. Thinking of getting a skinny fish, as it's a quad set up and looks like it might handle slightly bigger and better waves

my 7s is 5'9" and i love the size of it but with the skinny fish I'll hopefully be tackling slightly bigger waves and with a little less volume so yeah my question is any advise on size?

5'9" 85kg

cheers