I made a small test and I got much more than the 400Hz, nearly 1000 Hz (for packets of 60-bytes), and it works fine (please check the snapshot in attachments)... You may have some special conditions over USART/Data ... ?
I'm using the STM32F10X-128K-EVAL with STM32F103VB and the USB library is STM32_USB-FS-Device_Lib_V3.1.0 I'm planning to run this firmware on a STM32F102R8. Do you think I'm gonna have any problem with that? Thanks