Not the wisest decision, but whatever to each his own, with regards to pain. It has many dependent factors. Sometimes you'll get hit and just barely feel it shrug it off say your hit etc. Then other times it will really hurt just so many factors. But the biggest thing i find, is that when your in the middle of the game the adrenaline rush makes noticing the 'pain' of the BB very hard to do. plus unless your playing CQB your never really get shot from that close.
Thus is my personal experince i can't really speak for other people because each has their own threshold of pain/what they get shot by, example a sniper rifle shooting 450 with .36's or something like would be a lot more painful over a stock AEG shooting .2's
Which i bet you can obviously conclude...