I also have the OLM3 10 watt diode laser. It does all I want need. I would really like to have the mark blacker, but it's really ok now. The 20 watt, or even better the 40 watt would be somewhat better. Not sure it would do anything better than the OLM3 with 10 watts does, only the 40 watt would be MUCH faster. Some marks can take 30 minutes if they're very complex and larger - I've done one that was 60 minutes.
One BIG thing about the fiber would be the ability to do brass and other non-ferrous metals. Only problem with fiber is the price. The fiber doesn't cut wood, leather as well as the diode laser does - I "think" that is correct anyway.