Great answers, thanks guys.

I had noticed my archers seemed to be a little more effective as their valour increased but I wasnt sure if this was due to upgrades in weapons or variations in the enemies armour. But I do enjoy giving them a good 'Agincourt' style pelting before melee and it's so much better when they hit something

I think now I'll make sure my archers have armour upgrades so they live long enough to become really deadly with a bow.