This is just my opion and based solely on that. I like separate PSK and FAKs.

Here's why I fell this way...
1. A PSK sould be small enough that you carry it with you everywhere. That way it goes with you fishing, hiking, camping with out being a pain to carry.
2. FAK change depending on what you are expecting. A FAK for my car is not the same FAK I would take on a multi-day backpackig trip in the boonies. But my PSK is still the same for both.
3. Ease of use. Nothing worse than looking for one thing and having to wade through 10,000 other things to get to it. If I need FA stuff its all there in the FAK I don't want to have to pull out my Spark-lite, compass, mirror, lighter, purification tabs, andother PSK stuff to get to it. Same with PSK stuff, if my buns are on the line I don't wnat to be digging through FAK stuff (which would be on top because you se it more) to get the gear I need.

Anyway that's just my take on this.