Hmmm, at first thought, I'd say the Duron 1.2 would prolly be faster, but in gaming, memory/fsb bandwidth matters greatly, and the Duron runs at 200fsb while the TBird-C is 266fsb. I'd bet the 1Ghz-C will be faster in Gaming, but do keep in mind that with the right board, you could allways "overclock" your Duron to 266fsb. That's what I'm gonna do with my Duron 1GHz..
EDIT:AunixP35 is right as well. The T-Bird 1GHz AXIA's really were overclocking monsters, many of them hitting between 1.4 and 1.6GHz! So you make the call.