the contact resistance between 25um gold bondwire and pad ?

Someone as tried to measure and publish values, but in my personal opinion, the knowledge of the ohmic resistance of a bond wire contact takes a different way.
1) The contact join is gold to gold
2) Due to surface roughness and thermosonic mechanism, the wire connected to the pad has been deformed, to envelope and copy the contact surface.
Two thermosonic bonded gold "bodies" acts as only one body!
3) the wire feet is typically 1.5 times larger than wire diameter.

Conclusion: the contact resistance is every time negligible respect to the wire resistance.

I would point your attention to the wire inductance; very often the inductive reactance is very greater than the wire resistance.