Last season, half my matches were 3-5-2V & half were 4-5-1V and rotating between those two formation served me well.
To play 3 defenders you need very good defenders. I played 3 narrow at the back against 1 striker or sometimes against a weaker opponent, I've succeeded in playing 3 DCs vs 3 STs. Have to say that my strong defence last season has been key to winning the league.