How do you know if Speed is playing a big impact on Defense? If I have a guard with 90 speed and 30 defense does this make him as good as another guard with 70 speed and 50 defense?

Higher speed correlates with more steals, but defense has a higher correlation with reducing OFG%. In man and zone, I usually recommend avoiding defense that low (even at D3) unless the player brings a truly elite skill to the table, ie 90 speed coupled with ~90 perimeter and ballhandling for elite perimeter scoring. In press, that 90 speed by itself can be pretty valuable, in terms of causing more turnovers. Good luck keeping him out of foul trouble, though.

For guards, I rank speed behind ath and def in the defensive equation. For bigs it’s 4th.