the size of speaker wire has really no noticeable effect on the subs 0r speakers. there is like a o.1 db difference between 4ga and 14ga. so as long as your not trying to run a city......you'll be fine with 12-14 ga for all speakers.
heck that's even overkill, imo. we never use thicker than 16 AWG at work (Tweeter) when doing a system unless a customer requests it, and then its usually them asking for something stupid like 8 gauge speaker wire for their subs. 16-18 is fine for speakers, especially with low (<75 watt) power amps. 14-16 for subs is just fine.
just make sure speaker wire and interconnects are away from power and ground wires.