IMO the SL is just a resort board, not bomber enough to be a true all mountain board, but too directional to be freestyle. There are more aggressive boards in the NS lineup if you're into charging more difficult terrain.
If you're looking for something park friendly go with the Proto. Similar flex to the SL just with a centered stance which makes it 10x better for riding and landing switch. I'm 6' 185and find the Proto 157 is best for ripping and jumping. It handles resort riding just as well as the SL does.
If you're set on the SL there's no reason to size down, 158 all the way.