You're already getting 6# strength with Trilene. That's because 4# Trilene is really 6# line. Most lines on the market are stronger than what the packaging says.
My experience with P-line is limited. I didn't like the one I tried but can't remember which version of P-line it was.
There are lots of good lines on the market. Ask 30 people and you'll get 42 different suggestions. Having said that, I'd stick with Trilene XL.