From the link http://h18004.www1.hp.com/products/quickspecs/12199_na/12199_na.html here:
The chipset is E7520.
Some of the validated CPU from Intel are:
The best thing to do is to check with the HP Support, they will be the one who have tried different combinations. And you never know the board needs a specific bios for a certain CPU model.
All the best,