Ok, I'm gonna make up something which will cause argument but let's say there are 5 types of board and to have a board for every occasion you needed only a 5 board quiver. For the average person - 180lbs and 6 ft (I'm 5'11") how does this sound then: (assuming blunted tips on every board for ease)
Street. - 152
Park Freestyle - 154
All mountain Freestyle - 156
Groomer/carver - 158
Powder - 160
As a point of reference for someone wondering, maybe.....
What do you reckon? Cause I reckon I'd be worried about going for a 160 (162) board even for powder....but then, I don't know!
I'm 5'9" 150 lbs and the sizes you listed for are what I use at 150 lbs (I ride a Proto 154 for park, I have a SL 155-156 for all mountain, and my last two powder boards were 160).
I didn't mention it before... but in my opinion you could afford to look at boards a little longer. The longer board will give you more effective edge (let me know if you don't know what effective edge means), which will give you more edge hold and more control. With reverse camber, blunted edges and various construction profiles it is hard to give you exact number... but here are the ranges I suggest.
154-155 for street
155-156 for freestyle
159-160 for all mountain
161-163 for groomer carver
161-163 for powder board
Don't be afraid of longer boards - especially at your size (big and strong). Remember a 163 is only actually 2 inches longer than a 158 (has adding two inches an about .25 lbs every made something difficult for your entire body to move?). Also realize that a powder board typically has an oversize nose , meaning it's effective edge is shorter and so it will generally behave like a much shorter board. My Never Summer Summit 160 has an effective edge similar to most 155cm board and so it really rides like a much shorter board.
I have ridden around a dozen snowboards over 165cm and the longest board I have personally ridden is 178cm although I would say that such big mountain boards are generally unnecessary for most people riding in resorts I would say - especially with modern board tech and construction). It's like driving a car with 300-400 hp, it may take a little getting use but you know how to drive properly and don't panic you can do it. Are you the type of person who panics and slams on the gas pedal instead of the brakes in a school parking lot? I didn't think so.
Not that you would.... but you could: