I've seen several instances of people with the latest steppings of XP1600s getting into the 1900Mhz range
A for example, Chainbolt has a newer XP1600 stepping that he got into that range on
air. It was a AGOIA stepping, date code 0206. He could run it at 1974Mhz for 4 to 5 mins and do a couple of Sandra benches on before it got too hot and he had to shutdown do to temps (he was using 2.24V Vcore). Another guy with the same stepping and date code is running at 1910Mhz @1.85V vcore and watercooling stable (no heat problems).
So you might want to save your $$