I am a strong skier, 6'5" 175# (lanky).
I ride the 189 Made'ns at +5 cm, Rossi Scratch 120 bindings, Salomon Pro Model boots.
They are plenty, PLENTY big for me.
I would get a 179 at +5/+6. It will spin. It will be agile. It will still have so much surface area, you will float in pow np. You will get plenty of float AND be danker in the park.
Just my 2 cents.