It does not surprise me that 1333Mhz FSB chips can "unoffically" work with a 975X. Intel has not change the VRM specs for new chips since Conroe's introduction. The catch with 975X is that you have overclock the FSB to 333Mhz in order to run the 1333Mhz chips at full speed.

It all reminds me of how some users got P3 Coppermines to work on 440BX boards using a Socket 370/Slot I adapter and overclocking FSB to 133Mhz.

I think it is safe to say that 975X is modern incranation of 440BX.