Conservation of energy between two charged sheres

[Will]

conservation of energy between two charged spheres

We are given two insulating spheres with charges q1 and -q2 separated by a distance d. Using concepts of conservation of energy and linear momentum, I solved for the velocity of each sphere at the point of contact.
We are then asked if the spheres were conducting, would the final velocity be greater. delta-U for the insulating spheres is U-final minus U- initial = Keq1q2(1/(r1+r2) - 1/d)) meaning there is some electric potential energy remaing, because the center of spheres are still separated.
But when the two conducting spheres touch, they are in electrostatic equilibrium, right? So there is no more potential energy, correct? How do I write an expression for the delta-U in this case? I should get a greater value, right?

 

[HallsofIvy]

In that case, U-final would be 0 wouldn't it?

 

[Will]

Talked to my instructor today. He said that when the spheres are conducting, the charges migrate across the surface increasing the magnitude of E in between, hence higher V-final. He also said its not a simple equation anymore, but we weren't really asked for one, just to reason that out.