LPC4357 Ethernet through put

Hi
I am using lpc4357 based on MCB4300. Ethernet maximum speed is too low.
here is a part of FTP code which is using USB MSD as a data storage:

U16 tcp_callback (U8 soc, U8 evt, U8 *ptr, U16 par) {
  par = par;
  if (soc != socket_tcp) {
    return (0);
  }
  switch (evt) {
    case TCP_EVT_DATA:
      break;
    case TCP_EVT_CONREQ:
      return (1);
    case TCP_EVT_CONNECT:
      printf("connect\r\n");
      return (1);
  }
  return (0);
}


...

SystemCoreClockUpdate();
SysTick->LOAD = (SystemCoreClock/ 100) - 1;
SysTick->CTRL = 0x05;

init_TcpNet ();
socket_tcp = tcp_get_socket (TCP_TYPE_SERVER, 0, 1000, tcp_callback);
if (socket_tcp != 0) {
   tcp_listen (socket_tcp, 1001);
}


while (1) {
  usbh_engine_all();
  con = ((usbh_msc_status(1, 0) << 1) | usbh_msc_status(0, 0)) & 3;
  if (con ^ con_ex) {                       /* if connection changed        */
    if ((con ^ con_ex) & ~con & 1)          /* if device 0 not connected    */
      printf ("\nDisconnected Drive U0:");
    if ((con ^ con_ex) &  con & 1)
      con |= init_msd ("U0:");
    if ((con ^ con_ex) &  con & 1)          /* if device 0 connected        */
      printf ("\nConnected Drive U0:");
    if (con)
      printf ("\nCmd> ");                   /* display prompt               */
    else
      printf ("\nNo drives connected, please connect any drive ... ");
    fflush (stdout);
    con_ex = con;
  }
  main_TcpNet ();
  timer_poll ();
}

CPU is working at 204MHz.
USB clock is 480MHz.
in CGU all peripherals are connected to PLL1 and it is working at 204MHz.

download speed is about 4MB/s
(in FlashFS sample code I could achieve 9MB/s for read and about 8MB/s for write)

I've manipulate FTP_UFI.c just for finding the maximum speed on ftp in this way:

unsigned long size=0;
U16 ftp_fread (void *file, U8 *buf, U16 len) {
  /* Read 'len' bytes from file to buffer 'buf'. The file will be closed, */
  /* when the number of bytes read is less than 'len'. */
        size+=len;
        if (size>100000000)
                return 0;
        else
                return len;

}

I know it is not working properly but I've omitted time of fread for speed test.
in download progress speed is about 5.5MB/s. I think it is a disaster.

I've set it as a TCP server and through put is about 2% of 100Mb/s

this code is the same as my LPC1788 board and download speed on LPC1788 with SD card is about 2MB/s(it is usual) and as a TCP server is about 80% of 100Mb/s(is it so perfect)

I've changed SysTick setting but this is the most through put that I could obtain.

some critical definitions in net_config.c:

#define MEM_SIZE       2048
#define TICK_INTERVAL  10

Do you have any idea?