Dampening is useful if you like to go fast, ride in snow that is *not* powder or groomed powder. It is also useful for landing on jumps that are slashed/bombed out from other people heel-sliding down the landings.
I think the SL is a fine choice for you (I have both a SL and a Proto and I could only one board, it would be the SL, not the Proto).
Do you notice a big difference when your hauling ass between both boards?
How about jumps? I think my SL is pretty damn poppy but I imagine a decent more on the Proto?