Another post about board sizing :D

After some advice on a first short board, any thoughts appreciated.

I'm 5'10, 79kg (plus 5:4 suit), intermediate, competently riding a 6'8 40L Seaside and Beyond. Looking to work towards shortboarding.

I'm planning to buy a used 6'1 37.1L Firewire Sci fi 2.0, I am aware it is oversized and I will outgrow it, but I can just sell it on when the time comes.

Is this, roughly, an appropriate step down into short board territory? I've rushed to downsize before and wasted a lot of time, therefore I thought a more gradual step down might be more appropriate.

I typically surf fat waves, that can rage from waist to just over head high, rather than super hollow waves. I could ride the sci fi as a thruster for steeper surf or a quad for mushier which I like the idea of.