I put the below in my origional code and it reduced the upload time of a 253k jpg file from 62 sec. to 15 sec.
if (myFile) {
byte clientBuf[64];
int clientCount = 0;
while(myFile.available())
{
clientBuf[clientCount] = myFile.read();
clientCount++;
if(clientCount > 63)
{
// Serial.println("Packet");
client.write(clientBuf,64);
clientCount = 0;
}
}
// close the file:
myFile.close();
}