Allot of people will say that wire plays no difference (post this on audioreview.com and see). I have Kimber Kable 8vs and 4vs in a bi-wire config for my mains (Def Tech 2002tl and also for the centre Def Tech 2500). I found that it made a slight difference from the normal stuff (was noticeable). Do I have scientific evidence - NO (remember I said slight). Did it bother me to pay 10 times more - a bit, but I got over it(I think the Kimber's look much better as well). If you drop 5000$ Cnd for a 5 speaker set, with almost another 2000$ for a receiver (pioneer 45tx) and DVD player (Panasonic rp91), I personally think that you should not cheap out on cables. If your whole system costs 1000, then get the cheap stuff.
Just my 2 cents.

Oh, and I,m going to use 12 gauge in-wall for the sides and rears.