cams are a good way to make the engine sound really different to others as the have their own profiles.A mate had a set in the golf gti and it sounded like it was gonna stall when idle just because of the pattern of the cams they are a bit pricier than most engine mods but give a better gain in performance than most other mods but it should really be done with the the remap to make the engine work better with the cams
in terms of performance some say between 10-15bhp but it all just depends sorry i cant give a definate idea but its just the way mods work im afraid