thick keycaps feel more solid to me when bottoming out. The thinner the keycap the more flimsy they feel. You can tell if you type on a normal black widow and a backlit one, the blacklit has thicker keycaps and feels much more solid.
I'm with Danule on this. They also make a nicer more "clacky" sound when they bottom out. I actually removed my intial o-ring mods just so I could enjoy and appreciate the nice sound of the thick PBTs bottoming out.
Originally, I didn't like the sound of the ABS keys bottoming out, which is why I got it in my head that o-rings were going to be good for me. But with the thick PBTs, I'm all about the noise!