Problems with Scheduler_Update_Speed = NORMAL

[Pharaoh]

I found that setting Scheduler_Update_Speed = NORMAL significantly slow down all users, regardless to their settings (even when they are not limited).
For example: (have more than 1 example)
I hava a user with no personal bw limits, who was downloading in ~80-83kbps when Scheduler_Update_Speed = DISABLED, but when I set it to NORMAL, his download speed dropped to ~20-23kbps. I changed it back to DISABLED and his speed went up again and vice versa.
This happen on all versions I tried from 5.2.x and up. Currently using 5.3.4r
OS: Windows XP SP1 latest patches
Scripts: ioA, ioB, ioGui