I'm looking to get an external monitor, a Samsung 20" . It is 16:9 ,1600x900 I wonder will I have problem to get the optimized 1600x900 on it? I will be using the mirror mode. I've been using an old 19" LCD 4:3(died). I used mirror mode, and the LCD at ~1280 x 1024. I'm worry if I don't see the 1600x900 option in the display preference menu.