Ethernet2 (UDP) SPI transfers have a lot of dead time

Hardware Arduino Due
6

I certainly can post a complete program, it's not that I couldn't be bothered I just didn't realise it was the norm to post the entire thing. How much code is too much?

#include <Ethernet2.h>

// Edit the SPI speed in C:\Users\[USERNAME]\Documents\Arduino\libraries\Ethernet2\src\utility\w5500.cpp
//  to 28000000, 28MHz, line 25: (copy/paste the following is easiest)
//  SPISettings wiznet_SPI_settings(28000000, MSBFIRST, SPI_MODE0);

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
const IPAddress MyIP( 192, 168, 0, 10 );
const IPAddress Remote_IP (192, 168, 0, 1);
const unsigned int Remote_Port = 12345;
const unsigned int Local_Port = 12345;
EthernetUDP Udp;

char packetBuffer[UDP_TX_PACKET_MAX_SIZE];

unsigned long current_micros;

const int Testpin = 52;
void setup()
{
  Ethernet.begin(mac,MyIP);
  Udp.begin(Local_Port);
  pinMode(Testpin, OUTPUT);
}

void loop()
{
  const unsigned long looptime = 1000;
  const int EthTxBuf_Size = 100;
  byte EthTxBuf[EthTxBuf_Size];
  digitalWrite(Testpin, HIGH);
  current_micros = micros();
  Udp.beginPacket(Remote_IP, Remote_Port);
  Udp.write(EthTxBuf, EthTxBuf_Size);
  Udp.endPacket();
  digitalWrite(Testpin, LOW);
  while ((micros()- current_micros)<looptime)
  {
    
  }
}