Since you said your using it for the park, I think the 390s will be great for you. Also, the length issue is just a matter of preference. I think you'd be ok with a 156 if it was for 80% park use. I'm 6'3'' and ride a 166cm but I tend to stay out of the park for now.
EDIT: What i said about length wise is still true but I forgot about your size 11.5 boots. I have size 12 and I need a mid-wide to wide board always. Did you already buy your board or are you still looking?
2009 Never Summer Legacy 166cm (All mountain)
2009 Ride CAD Bindings
2009 Burton Ion Boots
2009 Forum Youngblood 155cm (Park)
2009 Burton Cartel Bindings
Last edited by $ickZ06; 02-06-2009 at 11:06 AM.