Intel Xeon X5355
The Xeon X5355 is available in three different sSpec numbers:
SL9YM and SLAC4 being B3-steppings and SLAEG being a G0-stepping just like this QWTM engineering sample. I'm not sure what the difference is between SL9YM and SLAC4. The G0-stepping has a lower TDP and overclocks better.
The G0-stepping was released in April 2007 which is about 2 months earlier than this engineering sample.
The X5355 runs at 2.66GHz and boasts 4 cores. A good performer in it's day.