I'm down to
Looks like these are better starting points...
Canon's recommended is around Radius=0.3, Amt=100-150, Threshold=0.
Depending upon your RAW converter you need to ensure that the converter is not sharpening the image during the conversion - if so then reduce your USM accordingly.
If you have PS CS2 then you may wish to give smart sharpen a try with 'lens blur' setting and similar figures to the above as well.