Ah, the post is about Medieval English Longbow, which IMO rules out Victorian and bamboo... but...
Well, yes, if you want maximum speed you'll prob go to as close to 5/8 as you can get away with and bamboo backed*... or build something other than a longbow.
That's exactly the problem with rules, people always want to push them to the limit to gain some advantage... what on earth a 5/8 bow with a bamboo back has to do with a 'real' longbow is anyone's guess???.... but it depends on the individuals idea of what constitutes a longbow.
That's one reason why I tend to shun societies and competion, they so often degenerate into politics or gamesmanship, neither of which are my bag.
Personally I've not seen many longbows that were pushing the limit, but then I only shoot field and the odd roving marks. Maybe on the target shooting line there are some.
I'd rather just plough my own furrow.
Personally I think the 5/8 is more than generous for a longbow, I don't think I've ever been in danger of going flatter in a longbow.
Bottom line is I make bows and I don't give a tinker's cuss what they get classed as! There is one bonkers society that would try to tell me that my old 70# self Yew isn't a longbow 'cos it doesn't have horn nocks
... do I care? Nah...
Del
*In fact I built a longbow close to 5/8 boo backed Yew, requested for a friend of mine ... fast as hell.
but by no means lime a 'medieval' longbow.
He wanted it 26" draw, but I only had a skinny bit of Oregon Yew left for the belly, so It was only marginally heavier/faster than his current bow. Thus he didn't want it and I kept it for myself... he was getting about 190 yards with his short draw, I pulled my regular arrows to 28" and they almost went out the field (240yards!
) look on his face was priceless! I'd love to see how far it would chuck a flight arrow.