It would seem illogical for the arrows to be faster with the heavier Turbo Nocks than they were with feather fletching. What makes you say that they are faster than feathers?[]

I have not shot these things, although it sounds like they are worth trying.

If you said that they were faster because they were dropping less, then I' d bet that is due to lowered FOC with the added weight at the back of the arrow. That and reduced drag may account for reduced drop. It is not really a bad thing if you are grouping well, as you seem to be.