I've found "sound guy's intuation" judging of speaker by the magnet size to be basically true bigger magnet = better speaker.
The same can be said for amplifier power ratings.
I always followed that rule too, but I just got a new set of subs with neodyum magnets on them. Each sub weighs only a couple pounds and the magnets are smaller than a hockey puck. They hit harder than the JL's I used to run 20 years ago. I really wasn't expecting much out of them, based on magnet size, but with a 300x2 amp pushing them, it's usually turned down most of the way.