The New York Observer’s Max Abelson reports a new high water mark in Manhattan apartment sales — a $50 million contract for a flat in the unfinished Plaza Hotel condominium. A year ago, a broker told me that if Blackstone Group chairman Steve Schwarzman put his 740 Park Avenue duplex on the market it would easily fetch that same figure. Just think, Steve, you can now ask $60 million, set a new record, put 740 back on top where it belongs, move into a studio in the financial district (I hear they have saunas and lap pools these days) and tell everyone you’ve done it because private equity’s gotten too big for its britches and you wanted to set a good example. Or maybe your old partner Pete Peterson will let you bunk at the Nelson Rockefeller apartment at 810 Fifth that he just bought from David Geffen for $37.5 million. Then you could sell a reality show version of the old sit-com, Bosom Buddies — and Geffen could produce. Synergy, dude! And think how happy you’d make the local realtors.