Yep. Mazda6 and Ford Fusion brakes are bigger and bolt right on aside from the rear ebrake cables mentioned above, and a cheaper option since there's tons of them in local junkyards. Speed6 brakes bolt on too but are aharder to come by and more expensive for the additional improvement that you get.
Because the fronts are direct bolt-on with no modification needed and the fronts do most of the braking, I would try your hand at Fusion/speed6 fronts first, see how they perform for you, and then consider upgrading the back after if you're still not satisfied.
Unless you're doing tack days or some sort of track racing, putting bigger discs on the front of a P5 on a daily driven street car is a waste of time and money. You're also adding weight to the rotational mass at the front, which slows down acceleration.
Another reason for putting bigger discs on a daily is the wank factor.