If your rotor is bent or warped then it's time for a replacement.
Silencer packing should be replaced as necissary, if you are asking than it is probably due. Blown out packing can effect power at all rpm. Before you go spending money on aftermarket parts, what kind of condition is the bike in? Time for new reeds? Maybe the topend is ready to be replaced? No sense in throwing speed parts on something that needs basic maintanance first.