I have a 158 SL and rode a 157 proto HD last weekend in 5-10". Going to take the proto HD out again today in 10-20". The proto is more fun overall, but without a doubt the SL floats better even with the shorter effective edge in those sizes. Both are great boards though.
I have not ridden the SL, but the 157 proto HD will float at least as well, probably better IMO. The caveat is that you need to take 5 mins to set your bindings back (SL has a setback built in).
Why does it float better? Because as ETM said the stubby upturned tip on a normal board doesn't work well in pow. Thanks to the blunted tip I really don't see this as an issue for the proto.
I have riden mine through very deep (50cm plus) and sometimes heavy pow with a minimal setback and I find the float to be very very good (for a non pow specific deck). Obviously a more pow specific deck will always work better.
The flip side of the float from a pow specific deck is what you give up in other areas. With a cheetah, fish, prior or birdman you give up a lot IMO.
The OP clearly rides ice regularly. He is also talking about a VERSATILE
pow deck that he can take through the jump line.
The proto is the best on the list for hitting the jump line and on ice.
We do not know how much pow he is talking about and my guess is that he doesn't need any of the boards ETM is suggesting for what he wants to do (apart from the powder snake which I like the look of).
The proto 152 is a very good option IMO, having said that the powder snake's smaller size (147) will probably work better for you with your small feet (depending on the terrain and depth of pow).
OP can you tell us more about where you want to ride, how deep the pow you ride is?
Is this board a 1 deck quiver for all occasions that also needs to do well in powder?
@ETM most people on here talking about pow will never see the depth you are riding nor the gentle terrain with long tree runs. You are also a very big guy and need much more board to keep you afloat.
I personally don't want a board that limits my ability to freestyle in the powder. I want to be able to spin 180s and land them, do powder butters, tweak out my grabs.
Big ass powder boards limit those options and I will happily give up a little float for some extra playfulness. I almost never get stuck and regularly blast past people on directional pow decks who don't know how to keep their momentum in the deeps. Not saying I could blast past your good self as you clearly know how to ride pow and ride a pow rocket monster thingy.
If its very deep I will go with a more directional board, but for me it needs to be at least 30cm or 40cm to warrant this. Lets be honest most people rarely see more than this and only a few days a year.