hey phil
recommend going a 7m drifter over the 8 if it is supposed to cover you to 30kn.
my mates on them (75-85kg) the last few years will even max out the 7m when it is really honking solid 25-30 (can still do it, but not great for wave riding as you are getting too pulled around), let alone 30+
maybe go 12m switchy, then 10, 7 drifters
i do similar with a 12m dice as my only lighter wind kite, 9, 6 neos for everything else
twinny occasionally to mix it up but mostly a couple of different surfboards ridden majority of time. even with that range though i think about going 12, 10, 8, 6 if the finances would allow

trust me, you don't want to be saying "the 8 will be ok, i'll just use a twin tip if too over powered for surfboard", cause when the waves are on...well, you know...