It certainly would not hurt going thicker, if you look inside most sub designers they usually don't use heavy awg wire but it won't hurt.
I promise, 14 vs. 10-ga. wire won’t make any difference for a 12 inch length. As Tony said, typically subwoofer manufactures don’t even use something as substantial as 14 ga. I mean, check this interior shot of SVS’s SB-12 sub. That’s probably 16-ga. wire at best.
I'm talking about the reverse, how much smaller can you go internal, considering how short it is. I will probably use 11 gauge from amp to sub and I was going to use 14awg internal for about 24".internal wire gauge doesn't need to be bigger than the wire gauge coming from the amp to the speakon connector on the sub. If you want to solder it's really easy. Get solder iron and a small roll of electrical solder for $10.99. RadioShack® 5-Piece Basic Soldering Set Catalog #: 640280
Does soldering give a better electrical connection? Lower resistance...?Agree with dsowens, you can always solder the wiring to the Speakon.