AEM gears have been known to slip, which could potentially destroy your valvetrain. Other than that, I suppose they're alright. As for how much power you can net with them, that depends entirely on how well you tune them on a dyno, as well as the other mods you've done. 10hp is possible, but not on a relatively stock engine. If we're talking about a SOHC engine, I doubt you'll net much power, but you['ll be able to optimize the cam timing to get the powerband where you want it.