4MHz output from Arduino

Guys,

As the discussion on the forum, I'm trying to generate VGA signal (color) with an Arduino UNO.

To avoid the nightmare of trying to set the correct times in a code taken from the internet, I decided to make this project from the bottom, generating the sync signals with the precise frequency.

The first step was generate the highest freq I could. Until now I could get 4Mhz using a code taken from this discussion: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1169088394

It works! The pictures are above and the code below:

/*
PortD - Arduino pins from 0 to 7
Pin 0 = D0
*/

void setup() {

DDRD |= B11000000; // sets pins 7 and 6 as output without changing the value of pins 0 & 1, which are RX & TX
PORTD |= B11000000; // sets pins 7 (hSync) and 6 (vSync) HIGH
};

void loop () {

do {
PORTD = B11000000;
PORTD = B00000000;
} while(1);

};