@vile If 'direct' mode runs stable for you, it is the better way, as it optimizes the plotfile within one work step.
For me it works well using 'buffered' mode, cause it plots faster. But i have multiple drives, and once one drive is plotted i start optimizing it. While i plot another one etc. but that way you need multiple drives and always free space for optimizing. 'direct' maybe takes some more time but is less work.
If you start plotting, you get very good nonces per minute, cause plots are only in memory, once the plotter starts writing plots to disk nonces per minute goes down ... and a little up again if finished and plotting to memory again.