No 1600x1200 on digital LCD
From MEPIS Documentation Wiki
If the picture on your 1600x1200 LCD monitor with digital cable does not look as nice as it should, fonts are ugly and the resolution is in fact only 1268x1024, even thought you selected 1600x1200 on the boot screen and your card is perfectly capable of 1600x1200, read on.
Try using an analog cable instead of the digital one (smaller connectors on both the display and the video card). Reboot and select 1600x1200. If your fonts got superb now, either consider the problem fixed (and keep the analog cable), or read on to know more.
If changing the cable did not help, look elsewhere, this page describes one particular firmware bug which does not apply to you.
If you want to verify that your LCD is not working in the optimum "dot-for-dot" mode but is interpolating 1280x1024 dots from the video card onto the 1600x1200 physical cells on the screen, look at letter "E" and move the window slowly up or down. Thickness of the horizontal lines in "E" is changing as it moves.
Then look at /var/log/Xorg.0.log and search for this line:
Mode "1600x1200" is larger than BIOS programmed panel size of 1280 x 1024
If it is there, you might be affected by a firmware bug in your video card. Due to this bug, exact capabilities report received from the monitor via the digital cable is misinterpreted and your computer believes that LCD is 1280x1024 only. With the analog cable, your computer cannot get that 'smart' because in cannot ask the LCD for details over the older analog cable. Then it just believes you and does 1600x1200.
This problem was observed with some nvidia videocards. Using some particular Option "ModeValidation" ... in /etc/X11/xorg.conf may help or not.