You'll definitely get a smoother bitterness doing all hopstand additions, but I don't perceive the IBUs the way the software lists them. In other words, you might not feel like you got quite the bitterness you wanted. I like a reliable 60 min addition to get a predictable bitterness, and the then steep the rest (for American styles). In terms of getting a smoother bitterness, I like Warrior or Magnum for smooth bitterness, Columbus (or Chinook) for a more coarse IPA type bitterness. Try the same recipe bittered with Warrior and you'll be surprised how much smoother the bitterness is.
EDIT - OTOH, there's no harm in experimenting. You'd still make a good beer. My only issue is the predictability of the bitterness.