The difference is the following:

The version "op" prints the estimation which Houdini uses in the search.

But it is of internal kind/size in which the estimation of a pawn is equal not 100, but 200. And all other parametres are doubled in comparison with Ivanhoe and other similar cursors. Therefore in the version "p2" the deduced estimation is divided through 2 so that a more natural value of an estimation is turned out.

In original Houdini the deduced estimation is a little strange and not having any relation to the reality.

Houdini 1.5a p2(32bit) - download

Houdini 1.5a op (64bit) - download

Houdini 1.5a op (64bit) - download