Personally I think the Powder Snake is better than the Sickstick. Same shape, but a more traditional core and flex profile. Just more oomph in a slash or popping off pillows.
Your 157 Nitro is going to be more than fine for 140lbs. As long as you've got a decent grade to the mountain you're at even if it dumps 4 feet that board is enough. Keep some speed and you'll plain just fine.