i'm planing when manly station hits 12kts.
i see a lot of sailors around who go big sails straight away, and most of them can't gybe cause everytime they stack its a big struggle to get going again, so they stop trying and end up sailing really long tacks and not really improving their skills. actually i plane before most of them anyway, cause the big rigs are so awkward and they never learn to pump properly.
even for me going from a 5.9 to a 5.7 has got me trying heaps more stuff, cause i've probably dropped a full kilo off my total rig weight, which is probably 15% of the rig weight, pretty significant.
i did have a 7m race sail and a 110 slalom board for about 6 months, it planned about the same time as my smaller wave/freestyle kit, and for sure it was way faster, and also powered through the lulls, but for me i couldn't justify all the extra gear for very minimal gain.
eitherway, the smaller sails work for me, and i sail as much as almost anyone here. if i got a 6.2-6.4 i'd probably get going as early as the guys on 7.8s, i already got the guys on 7's covered