Very, very different sounds between those two. The P series is the classic SP horn (3 chime) and Southern Railway (5 chime). The K series plays a higher note, and is the more common horn in modern railroading. That is putting it very simply. I like both varieties, and find enjoyable qualities in each.
The history section in this Wikipedia article is pretty good at laying out some differences:
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en.wikipedia.org]
And it is hard to top the Five Chime Consultants website for sound samples to know what you are hearing when the horn blows:
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atsf.railfan.net]
Mike Derrick