It would be helpful if the program had pre-sets built in, as many games do ('High Quality', 'High Speed' etc.)
The advantage to keeping all maps loaded is that it saves having to wait every time you pass from one map to another, of course, but it will mean a performance hit since all the maps need to be stored in memory. Keep it off.
Multisampling (Antialising) refers to the graphics card rounding off jagged images by rendering polygons more than once or something like that. It is a big deal for lower end cards, and really old ones can't handle it at all. If you want to raise fps, keep it at 0 or a low number. (The higher the number, the more passes the graphics card has to make). Don't check 'multisample for quality'.
I am not quite sure what texture downsampling is, but from the name it suggests to me that a texture of say, 160x160, is reduced to half, quarter or whatever. This means that the textures (the 'paint' on the polygons, like bricks, faces of characters) etc. will look worse - less detailed, more blurry. But, you will save a lot of memory in both loading them, and it will require less of your system to render them thus resulting, I think (someone will correct me if I'm hideously wrong) in a performance boost.
If fps is a real problem, there's nothing quite like reducing screen resolution and color depth, but please check other forum posts (possibly in the problems in game list) because I understand that the CS engine is particularly bad: this from the sticky on there ('known fixes'):
Here are a few things you can do to help your system handle problems on your side:
* Update the game and your graphics card drivers.
* Don't use 16-bit color depth. CS just doesn't work well with it.
* Try enabling the adaptive distance feature in the options menu. It'll try and maintain a framerate by not rendering farther away objects.
* Try lowering the graphics settings in lower right of the setup application.
* You can always try lowering the game's resolution in the setup. If you can't play with 800x600 or even (the horrid) 640x480, and you've tried everything else, ask for help.
See here:
http://hydlaa.com/smf/index.php?topic=21503.0Good luck!