EXS 24 Logic Sampler Users Group

I've searched the lists, and I still feel very unsure about how to manage
system memory.

Logic 5.5, OS 9, EXS24, Atmosphere, etc. on a powerbook 667 with 778 meg of
ram.

I have the preferred size for logic set to 200,000, and locked. But tonight
near the end of a project with maybe 5 exs instances open and one (big)
atmosphere instance, the program begin to move very ponderously. Took a look
and sure enough, the program had 360 some meg of memory, but the bar showed
that it was almost all used up.

Now. Isn't the program taking new memory every time I open a new exs
instance and load a sample? The only thing I have any control over is how
much memory to give it at boot up, no? And if I give it too much, there will
be less left over for samples, is that right? I don't know, couple that with
the fact that atmosphere draws it's sample memory from outside logic, from
the remaining free memory in the system, and I'm just pretty much thoroughly
confused about how much memory to give Logic in the first place.

Does it depend on what kind of softsynths I want to use per session? Should
I be tailoring the memory assigned to Logic per session? And if so, what
about in most cases where I don't know in advance what I'm going to be
using?

I know, I know, OS X. But I have to get through the next few months on OS 9
still. Can anyone shed some wisdom?

Cheers! 

Darcy