What perfmon counters should I use to get the fastest restore possible on an idle system?
If you are running Developer or Enterprise edition, consider restoring from a database snapshot rather than a full backup (https://msdn.microsoft.com/en-s/library/ms189281.aspx).  This can also be less resource-intensive than a full restore.

The time needed to revert from a snapshot is largely proportional to the amount of changes made since the snapshot was taken so it can be significantly faster than a normal restore in many cases.  Like a regular full restore, the log is initialized so keeping the log size small will reduce the restore time.