I use bbb trick to leech on 10mb .se, i have ADSL 1mb.
With 5.1.x i am on the max : 125KB/s
With 5.2.x, speed max is 60-80KB/s
I use same ioftpd.ini for 2 version, i have try to config ioftpd.ini with bandwidth control disable, the result is the same.
I have kickout all user from site for my tests
and its seems 5.2.x version have performance problem.
Best regards.