Re: what size speaker wire??????
What he said, but it if you have a heavier guage laying around (18 or so) you can use it- basically you can't really overkill speaker wires (within reason).
18ga is actually bigger. The larger the wire, the smaller the gauge... Just like with earrings!
However both of those guys are correct. Its NOT going to matter. Use 20ga, 18ga, 16ga, 14ga. Powering 6.5s wont even overload even the smaller 20ga. As a average, 16ga is the norm. You can run 6.5s, 6x9s, 10s, 12s, 15s, etc! Amp'd or not! The only time gauge is a concern is when your choosing your Pos and Neg leads that supply your Amp. Then you would want to go "Big"
As a comparison, in my car, I have a 1000watt Alpine amp powering 2 Infinity 12s with 16ga SPEAKER wire. In my boat, I have no amp, with 2 6x9s, and 2 6.5s, both coming strait from the radio with 16ga SPEAKER wire. Actually the only time I've seen smaller wire used was with stock vehicle speakers. I've personally seen both 20ga, and 18ga used.
Do yourself a favor, get a roll of 16 gauge speaker wire from ebay, walmart, where ever, and wire til your little heart is content. If you ever wire any other speakers, you can use the same wire no matter if its Amp'd or not, or for small, med, or friggin huge speakers.
As a note... Although it will work fine, I suggest using actual speaker wire. Any type wire will work, but speaker wire does supposedly have its advantages (although very few), PLUS it looks better being clear and all.
Good luck!