Nous adorons the duplex at 165 Commonwealth Avenue, what with its Gilded Age finishes, its hardwood floors and ceilings, its deeded parking. It looks, as we put it last month, like the kind of regal place fit as a setting for a British murder mystery or a spoof on the foibles of the aristocracy (such as that Monty Python sketch where Oscar Wilde meets the Prince of Wales). Well, the reason we were typing about the 3-BR, 2.5-BA then was that it had been price-chopped by $125,000. Add another $146,000 to the subtraction as of Tuesday. The 2,653-square-foot spread is now asking $2,549,000.