First, you really need CL rated wire in the walls. Other wire would not pass inspection, if they actually look it it. In any case, CL2 and CL3 wire is readily available, so why take a chance. Cl3 takes a higher voltage than CL2. Either will work in your case, but why not go with CL3 if possible.
I have used Belden 12 gauge CL3 in wall wire and been very happy with it. There is no reason to go with 10 gauge at those distances. 14 gauge would also work, but for the modest price difference I would go with 12. Running 14/4 makes the run a lot easier if you are running to a common spot like a volume control. If you are running directly to the speakers, then just use 12/2. Make sure you speaker wall plates and/or banana plugs take 12 gauge. It is a pain to try to get 12 gauge into a 14 gauge hole. Depending on decor, you can also run the Belden wire from the wall to the speakers. For my theater, I just run the wire out of the wall places with the wallplates meant for home theaters, either the recessed ones or the bump out ones.
If cost is a concern, Monoprice has 12 gauge CL2 wire. I have also used it and it worked fine, but I have typically used it only for secondary speakers, like background speakers in a second room. You might consider it for surrounds, if the runs are long.
Belden cable is also usually available at local volume electronics stores (not big box stores), but you may have to buy a set size, like 100 ft or 250 ft.
For the sub you can run Blue Jeans Belden 1694A with RCA connectors. I think it is CM rated, with also works in walls.
I run the Belden speaker and coax in my theater and am very happy with it.
Before investing in expensive wire, I would get some Belden and try it, not in the walls, and see how you like it. At 50 cents a foot, it is a cheap experiment compare to $1000 for audiophile wire.
