which size of OFC loudspeaker cable should I use?

["reellifetv@xxxxxxxxxxx" <reellifetv@xxxxxxxxxxx>]

Sorry if this is a little bit off-topic, but....

I'm currently wiring up my house, taking advantage of the floorboards
being up.  in a couple of places I want to lay in some speaker wire, to
connect the amp at one end of the room to the speakers at the other
(say 5 metres separation).

My local cable supplier is offering OFC loudspeaker cable, in a choice
of sizes - 1.5, 2.5, 4 or 6mm2,

the 6mm sounds like it's for stadiums! So what should I use - 2.5 or 4?

Many thanks for your help.

Chris