[ QUOTE ]
And as for Doom III (and I assume Quake 4 as it uses the same engine), it has single textures that are >512MB fully uncompressed. If you really want to find out what you can live with in terms of hardware performance for Quake 4 I suggest you read
this. It should give a general idea of Quake 4's performance on various hardware.
[/ QUOTE ]
Or you could just get the game and try.