did you read this thread?
https://forums.modx.com/thread/80377/give-modx-some-speed
also take a look at
http://www.sterc.eu/modx-blog/modxpo-contest-winner
you use phpthumbof, so the first hint also may be helpful. Unfortunately the exact description regarding the cron job is missing until now. Hope, they will share this optimizations soon.
Manfred
