I think I have to eloborate. What you said is best if achieved. But..

Getting a flat piece of metal sounds exciting - but very difficult, if not possible.

Even after getting a flat piece of metal, getting it SMOOTH is a task by itself. You need to do fine lapping or grinding or polishing.

If the above is not ensured, then when two "flat " metals are bolted together, the contact between both is at the crests - which basically is a point contact.

In such a situation the paste acts as a filler in the valleys "improving" conductivity.

Maybe I oversimplified the point in my first post. Not that you will have a thick layer of paste beteen the chip and heatsink! Apply a smooth layer and press. Wipe off the extruded paste from sides and when bolting, use an amply sized washer to spread the clamp force. your chip will simply love you for that treatment.

Raghu