The smoother the face, the less friction between the lapped faces. Vacuum causes a heat problem between faces. Condenser hot wells run under a vacuum. Evaporators often run under vacuum. High soak temperatures can cause a seal failure This becomes important after the cooling or flushing is shut off when the pump is stopped.
Some metals are better heat conductors than others.
The conductivity of stainless steel is poor compared to carbon steel as an example. The stuffing box design is important. The inside diameter should be as large as possible. A steady flow through the stuffing box is very important. Suction or discharge recirculation is necessary if you do not want to flush the product with a clean lubricant.