cant point to the specific ones available but I have not heard of any getting 20-30hp. Maybe 2-3 (k maybe not that bad) Cant remember exact numbers but from what I remember there was one option with possible small gains and another that was no gain/slight loss.

Honestly if you don't have much else done, move this down to the bottom of the list and pick up something that will give you more hp/$

[edit] did a search and the VRP headers TVT was talking about were $1300 for ~ 10-15...