I like both. So yeah it's pretty much whatever you like. I'd say if you are more flow than doing tricks and stuff, get a 4.5. But IMO, 4.o is way easier to whip.
It's preference. You could try 4.5, and worse case scenario, you find someone with a 4.0 to trade with, or loose a few bucks by selling it and buying a new one if it's really that bad. But for me, the second I stepped on a 4.5 deck I couldn't go back.