Polarizer dilemma

[jimmy_racoon]

Currently have a Canon 70-200f/4L IS and 17-85.
Both use 67mm, so a B&W CPL is what's in my kit now.
Just picked up a 17-40f/4L that uses 77mm thread.
Would it be better to get another B&W CPL (77mm), or get a 4x4 polarizer for my Cokin P system?
Also, any recommendations on a 4x4 polarizer?
Cheers