I've caught Defraggler pegging my CPU I noticed this because it was taking longer than usual to defrag a few files.
I checked the CPU load after pausing / stopping but the load remained high (with 3 highly active threads).
I restarted Defraggler and it returned to normal so my files defragged at the regular pace.
So this is just a tip for anyone else experiencing very long / slow defragging.
Pause Defraggler and check the CPU load, if the CPU is being pegged restart Defraggler.
Richard S.