if you look around at MD you will find data. Bill putnam did a write up on them. gained ~20hp.
there was also some threads about people gaining more hp with stage II but you have to do valve springs then. It is however recomended to do valve springs on either grind.
You will need a tune either way to dial in the idle.
so if i buy them for 650, thats all i need to pay rite?, also if i already have a predator i cant use thoese settings cuz i need to config it after the install rite? what would u recomend doin durin an install thx