PC is Power Compact. CF is Compact Flourescent. I think they're the same thing.
I've got a 4' 2 x 65w Coralife CF over my 135 and it gives off plenty of light.
The K rating won't really reflect the strength of light but the color rendering index. Bulbs with a 4500-5500K rating tend to be more pink/yellow while the ones in the 8000+ are more blue/violet. The ones in between are more yellow/white.
Personally I hate the pink/yellow color the lower K bulbs give off. I don't like too much blue either as it does nothing for the natural colors of the fish.
Anything 6500K-8500K is nice.
When it comes to standard flourescents I highly recommend ZooMed Flora Sun flourescent bulb. It's a 8500K bulb that gives off a violet hue but really brings out the natural colors of fish and plants.