Sam, I own numerous types of sanders, and I own both models that you mentioned in your post. I've owned both of them for years, and I couldn't pick one over the other for a favorite. Both of them are top of the line sanders, and one works as good as the other. Actually, I own three orbital sanders, along with the two I already mentioned I own a Porter Cable OS also. It is cheapest of the three, and it works as well as the other two. But, it isn't as nice to use as the other two, it just doesn't feel as good in my hand. If your looking for a sander to sand fret work with, you should be looking for a good quality detail sander. The type that has a triangular shaped sanding pad, it's the type I mostly use on fretwork. It does an amazing job, no matter how fragile the piece is. The detail sanders don't cost a lot of money, and they are great for getting into tight corners. It would be worth your time to look into the detail sander, they are the most gentle type of electric sander there is.
Len