The gauge of speaker wire mostly depends on the impedance of the speaker and length of run, not the power of your system.
16ga is adequate for just about any home application, but many people use thicker wires for asthetic reasons or peace of mind.
Yeah, in most cases jumper cables, er.. I mean speaker cables are overkill, but nor are they harmful. Except, in some cases to your wallet, or unless they're so heavy or stiff they damage your speaker or receiver terminals.
You could either get some type of connector to put on the ends, or merely trim off enough strands so they fit. Just be sure you don't have any stray strands (they can be hard to see) touching the other terminals or the case of the receiver.
Personally, my front and center speakers are wired with 12ga (~35 feet and the speakers have low impedance dips), my sides and back speakers use 16ga because the distance is less and no low impedance concerns.