1.2 from an 867 sounds a little ambitious. The later your machine was built in the production run, the more OCing mileage you are likely to get. The first three numbers in your Macs serial will tell you the year and week (respectively) your Mac was built. Compare this to the release date of your model and you should get a decent idea of how far you should risk OCing it.
The 867 Ti was sold from Nov 02 to Sep 03. So your serial should be between QT240-QT333. Or thereabouts. I could be wrong about the QT part.