With Shockers there's a slight increase in velocity when a NDZ manifold is installed (I didn't really notice with mine). However it's so minute that I can't imagine that's the reason for no FSDO, it has to do with the better design of the Nerve.
Even a Shocker owner said that the Nerve is designed better, if that doesn't answer your question, nothing will.
Ur in the nerve forum so ur gonna get alot of votes for nerves
I own both a shocker and nerve, the nerve has the same performance but way better maintnence, the shocker is barely lighter without a barrel, the trigger guard on the shockers r smaller then the nerves, which is bad. The shocker is barely shorter than the nerve in heigth, and the nerve is 125 dollars cheaper, so get the nerve, its worth it
99% of us will say ZOMG nerve is teh ****, and 99% of the shocker forum guys will say the same for the shocker. try them out, they're both great guns, and anyone that says otherwise is an ignorant spoiled brat. you'll be able to tell which one you like better instantly after shooting them both. I personally like the nerve more (partly because of the price and ups it comes with), but some people like the slightly more compactness of the shocker.
Best of luck.