I think I've graduated (or maybe soon) from being a rank beginner wingfoiler and I'm thinking about my next step for gear. I'm 173 cm tall and 68 kg, and I have a Naish hover crossover 120L (223cm long and 76cm wide). It is a great beginner board but it is huge and heavy.

I'd like to maybe drop down to a smaller board - been looking at Naish hover wing SUP, but also have read about how hard it is for knee starts and general stability on the smaller boards (under 95L). I'd also like to use the same board for prone foil surfing as I now do with my crossover, but that isn't the primary concern.

Naish site says that 40L is "ideal for riders up to 154 lbs/70 kg", and the 40L is 142cm x 53cm. That just seems nuts. I don't even ride shortboards that small.

For skills, I still can't foil gybe, but getting up and staying up is no problem. I guess I'm still a beginner but the 223cm board is starting to feel giant and unnecessary. I have the Naish s25 5m wing and a 1650 foil.

Thoughts and thanks in advance for any advice. You are all really inspiring in so many ways.

Possibly?
You are very lightweight. A 85 liter board is considered big for your weight.
You might have read the Naish surf foil site...paddle out to surf in, not wing out and back.

85L board will be easy for you to manage at 68kg, including knee starts.

I am 105kg on a 110L or 95L board. The 95L is a pain for me but the 110L is so easy.

I am 72kg.
Went from 105L to a Naish Ultra Hover 85L.
Knee starts are easy to learn.You will wobble a bit but once the wing is overhead and sheeted it's job done.

The foiling feels much much better on a smaller,lighter board.

I am not interested in even smaller because 85L allows to sail home even if the wind drops a lot.Which happens a lot here.

I have used it for prone surfing, cannot really duckdive it but being so short i can bury the nose and punch through.
I look for soft, waist high conditions anyway.
It paddles nicely with all that volume and the width is fine,not a problem.

Whatever you get,a bottom handle makes carrying board&wing a lot easier.

You will do well with approx 85 L dedicated wing board

You guys are awesome - I really appreciate the advice.

I am 85kg and riding a 95l board at similar level to you. I thought I made mistake the first time out. 2nd time realised it is doable and then was away.

We all need a challenge.

I'm on the same kinda of boat haha +40 litres. I would stick with it until you can gybe both ways. Well that's what I'm doing. Having a bigger board will help when you drop off the foil when gybing on your bad side.

I'm tempted to go smaller and try winging on my -25 litre proneboard as I'm doing mini downwingers and running back up the beach with a prone board -25 litres is effortless.