It does depend on your rod as well. If you're using a normal match-type rod then 6lb is way too heavy for the rod. I use a Daiwa 14 foot Aqualite with 3.2lb mainline and have landed chub to nearly 5lb (4.14 ... dammit
) from quite snaggy swims.
You just can't bully the fish with tackle like this ... you have to persuade them to the net. These rods do have a surprising amount of power as long as the tackle is balanced.