[ivymike1031]

Spinalfury, an underdrive pulley is not going to have the same effect as an adjustable cam sprocket. The most important thing that an underdrive pulley does is reduce the rotational speed of the accessories, thus reducing the power that they consume (and possibly how well they perform). Any change in inertia is going to be far lower in significance than the reduction in "parasitic" power consumption.

The most important change due to the adjustable cam drive sprocket, of course, is adjustability of the cam timing. Inertia changes at the cam are about 1/4 as important as inertia changes at the crank (because of the speed ratio), and we're talking about a tiny change anyway, so I wouldn't bother mentioning how "light" the cam sprocket is. The most important factors that I can think of are: precision of adjustments, permanance of a setting (doesn't slip to a different setting while running), durability of the part, and general fit&finish of the part.

I do, however, take exception to the statement that "reduced valvetrain weight wont make a noticeable difference in performance." From the context it is clear that the author was referring to rotational mass (inertia) of the valvetrain, and from that perspective his answer is correct. In general, however, reduced valvetrain weight (if it doesn't come with a sacrifice in stiffness) will improve dynamic control of the valvetrain. This means that the engine might be able to rev higher, and that the valves will follow their intended lift profiles more accurately at the higher end of the rev range, both of which can mean better performance.