Approved PSU when non-OC but not approved at OC speed?

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The Antec PP303X that comes with my SX830 is approved for T-Bird speeds up to 1GHz. For speeds beyond 1GHz they recommend the PP403X, a 400 watt PSU. If I OC a 900 chip beyond 1GHz will I run into problems due to a weak PSU? Does a 900@1200 draw as much power as a 1200@1200? Or is this one of those "try it and find out" kind of questions? Or is this basically a non-issue?