Speed Infusion 11 does not work

Uh what are you smoking? It works for Buccs. When I use Barrage with just my level 11 SI it seems a bit slower than if I Barraged with SI AND Booster.

Read. Please. You're interpreting the information very, very wrong.

I believe the peak speed is Faster (2) (correct me if wrong). Night Lords are already attacking at that speed with their own Booster casted, so of course Speed Infusion won't affect them. And if you're already attacking at Faster (3) with your own Booster, you probably won't even notice any difference with Speed Infusion. Warriors notice/benefit from it the most because they're attacking at slower speeds than other classes.