Your main concern is the aspect ratio. Old games were all 4:3. Newer games all have widescreen support 16:10 or more commonly 16:9. Unfortunately widespread widescreen support havent existed for as long as I would like with even, as far as i know, gta 3 not supporting it. However, If there is one thing that I have learned from gog is that if a game did not support widescreen originally, then somebody somewhere as made it his business to create support for it with a patch. And it usually works pretty good. I remember searching everywhere for a decent 19" 4:3 monitor specifically to play games without widescreen support but these days I don't bother anymore. For example: fallout, planescape torment, arcanum and dungeonkeeper are some of the games which I managed to play widescreen without a problem. So rather stick to your, probably newer, widescreen monitor. Newer monitors have better contrast ratios so the games look better in any case.