Dave,
Assuming your talking about SMAW with a 1/8 inch electrode the 180 synchrowave will do just fine. It takes less than 4 minutes to finish up even a 5/32 electrode at 150 amps, which would appear to be overkill anyhow on 1/4 inch boilerplate. GTAW? Well, it would take a pretty big pipe to necessitate walking the cup at 150 amps for over 4 minutes.
However if you're investing in a professional shop machine for the long term, the synchrowave 250 is the proven champ. It will provide much more flexibility; furthermore in my experience the things are virtually indestructible. We have over 20 of them, some over 14 years of age, which have never blown a circuit board or even needed the HF points replaced. In my opinion anything less than the synchrowave 250 is a garage machine, which is fine if you're in a home shop situation.