I wonder how many pages this one will end up

Hi there Ioz, in waves under 6 foot (2x overhead) weight is quite important for performance IMO. Most guys that compete are riding SUPs in the 5.5 - 8kg range with grip/wax fins on. Lighter the better for high performance surfing in 1 - 5 foot.
Even some of the pop outs like the smaller carbon Starboards are as light as customs, which are around 5 -5.5kg with out fins/deck-grip.
Of course these types of boards aren't going to be as durable as a 10 kilo job but if you keep em maintained (ie fix your dings) and they don't take water they will last for ages.