To save you from being flamed up later, lol Someone will tell you to use the search bar.
But I will break it down to you (from my knowledge, that is)
No one knows exactly what Billy Wing does to a BWinged NT. That is his trademark, if everyone knew he wouldn't be doing it anymore. But from what I hear from around the forms is that each little mod he does is different from gun to gun. But whoever sends their gun in to get it BWinged usually is pleasantly surprised at the difference, mainly the consistency. On average an un-BWinged NT will probably get +/-15 with FPS. A Bwinged NT I hear from shoots around +/-5 FPS. This will probably not get you an extra pod or what not, but it will be more accurate. You also still have to factor in the things like bore size and paint.
I hope this helps you, and this is what i read from another form, so it is only knowledge/rumors I read from the forms.