Long run cable advice for surround spks.

I need to run 30-40 ft. cable lengths to each of my rear speakers in my 6.1 set up. What wire should I use, brand, wire gauge, etc. to maximize sound quality.
I have a similar length run to the rear speakers in my HT system. Since the rear speakers are for fill, and in most cases are reproducing a somewhat restricted frequency range, you don't need to spend buckets of money on speaker cable. Monster Cable makes a perfectly satisfactory range of cables for $1 - $1.50 per foot, with several that are made for runs underneath the floor. If you want to get a little more upscale, my other recommendation is Kimber Kable 4VS ($3 per foot) or 4TC ($7 per foot).
I'd say go with the Kimber Kable. Even the 4PR or 8PR will be better than the Monster Cable. I used Monster Cable for my surrounds for several years, and the cable fell apart over time. I've had an equally long run of Kimber Kable 8PR going to my sub and it still looks brand new. I replaced the Monster with Kimber 4PR.

Also, the Kimber is braided to reduce noise pickup, if that is a potential problem for you.