47 mil, I agree it's tougher to have good D. I usually want to be able to guard every position with a 75-80 defender or better if possible (I'll admit, that number is somewhat arbitrary - I have no reason for it in particular other than it's about what seems to work). That usually requires 2-3 defenders at that level or higher. I prefer not to have defenders below 40 at all, and not more than 4000 or so minutes of below-50 defense.
I also prize position flexibility in all leagues, but especially this one, for defensive purposes - it's a lot easier to hide Ray Allen's 40 D when he can play the 1, 2, and 3 at 100%. Just remember when you're taking good defenders that can guard multiple positions, it doesn't help any if the other guys on your team can't - i.e., if you have Nance as a 100 defender at the 3, 4, and 5, but none of your big men can flex over to SF, Nance will always guard SF and you won't get the benefit of his D on any 4s or 5s.