Turns out it wasn't the power supply after all. Was a driver conflict. BFG tech told me wrong.

I've swapped between nvidia cards in the past without issue, but this time I had to remove the drivers via add/remove hardware and then reinstall.

So now I'm sailing on the 9800 GT OC, though I had barely gotten started when I got tapped playfully on the shoulder by my wife, hit DNP, /quit. Which means when next I log on I'm likely to be mobbed by Gordunni.

Still might aim for an updated PSU for christmas though, as a present and to go modular cable.