It would be a BIG if for me. I have landed Tench to 11 pounds on a pole, but I would NEVER intentionally fish for big fish using one.
But thats just me.
As heavy as will still get you bites is a short (and a bit glib) answer. Think about 0.18mm line (7.7 lb in Silstar Matchteam) or even (and it's not everyone's choice) braid straight through at about 8lb or more bs.
Make sure the pole and elastic are up to it - 16's+ laccy. I use 18's. That will land 5 lbers easy and keep them away from snags.
Yes, Rik's right - braid tends to fray on a spade end. Even with an eyed hook, make sure the eye is well closed and that if there is any sign of fraying you re-tie the hook.
The other thing about braid is that shot don't grip well on it - they either slide about or pop off when you get a fish. I've just got some Double Cut shot, which seem better for this.