EVO is softer than SL but compared to Arbor Draft for example, it is stiffer and harder to make it playful (relative of course)
if you want to jib and ground trick, i suggest arbor draft. if u prefer more jumps and land those big booters, then westmark.
otherwise, i'd say westmark for now - only because you already have a SL
if you are going to sell SL then buy EVO. i too love NS quality, construction & finish. it also seems like you still want all mountain capabilities. finally, like NS's dampering system better than Arbor's. so it feels good when landing jumps and not feel to much chatter. I don't think you can go wrong with either choice to be honest with you. you might have to go with the board that gives you better value $ wise.