Me, if I were to take the numerical bonuses off of items and put them on characters, I'd probably put them at 3/8, 13/18 & 23/28, to spread the boosts out a bit. I might do that on my next campaign, even.
The character builder will get in the way of that, because the power attack cards will assume that your magical items will have a +x on them. The workaround would be to not assign your weapon to the weapon slot, but then you wouldn't have the information on how the power and the weapon work together.