Colours on graph changed to order in the rainbow scheme. New test still running (crash point never certain, but shows same effect - cache increases as free decreases, and eventually swap gets used.
At this point, I've no idea how long the simulation will continue, other than at some point a crash and stop of acquisition WILL occur.
Also redone the previous text file to show the plots on the same colour scheme.
Without drop_cache:

With drop_cache: