With 2 MB chipram and 4 MB other memory you should be able to run the most games. Some would need 8 MB or 16 MB other memory. But that are only a few. As DamienD mentioned the readme's usually tell you the memory requirements. I think you want to use the PRELOAD feature. So don't save with RAM. E.g. MonkeyIsland2 uses around 9 MB for preload. BloodMoney 2 MB, Beast2 also 2 MB and Beast3 3 MB, Lemmings2 2,4 MB.
While thinking on upgrading to 3.1 you might think about 3.1.4.