Setting highlight for glass so it doesn't look grey

I usually set the whitest part of the image to 5/4/4/0, but this is making some product shots of glassware (ie wine glasses, glass trophies) look grey.

Does anyone use a different mix to C5 M4 Y4 B0 for the highlights? I don't want there to be no colour in the white area as it will look blown out.