Well . . . I don't believe aftermarket mufflers add significant power increase across the rpm spectrum in comparison with OEM mufflers; certainly, with nominally stock engines.
As to, weight-saving, a few pounds to a 400+ pound motorcycle won't produce significant handling improvements, nor mass reduction, seems to me (a half-gallon less fuel in the tank will do the same weight reduction).
Now, as to noise . . . just sharing my own experience: My WINGS muffler (made in Silesia) is lighter by far than the OEM muffler, and sounds GREAT, on my KTM690! Don't know if it has the "db" core, or what, but . . . it sounds good, WITHOUT objectionable loudness.
Someone lusting for muffler weight reduction, and sonorous, lilting (but discreet) sound for their KLR650 might consider WINGS. Reportedly, great customer service and prompt shipping from darkest Silesia.