As the table that wid provided shows, if your 30 foot runs are to 8 ohm, or 6 ohm, speakers, you should have no problem. If you're doing a 30 foot run to 4 a ohm speaker, you might. I don't really know if there would be an audible difference if you went with 12 gauge wire, but I doubt it. I use 12 gauge, just for the peace of mind it gives me.

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton