i'm looking for 390's as well... but i refuse to hijack this thread!
eh, you don't think board size has anything to do with height at all? I know weight is more important, but I mean my buddy is 6'1 (6 inches taller than me), but weighs the same as me. I think a 151 would be a little small for him, even though we weigh the same.
Reguardless height doesnt have an effect on the flex you could apply. Physics wise weight is the biggest variable.
I have another buddy who just started snowboarding, who is a little heavier but a good amount taller than me too. He's probably around 6'1 and weighs 170, you think he could ride a 154? I have an old, pretty stiff burton jussi that I've been trying to get rid of, and I'm sure he'd buy it from me if I told him it's big enough for him.