Remember: A dress code is not a prison sentence, it's a guide -- your own handy compass to steer you to where you want to go anyway! Look for the clues in office literature and on the persons around you and follow the signals faithfully.
A day off will take you way off course, so be consistent.
Get labeled for your excellent work, not for an iffy work wear choice. Frumpy, Sexy, and Sloppy sound like the clueless cousins to the Seven Dwarfs, not talent-in-waiting for the job you deserve.