256mb is what I ran when I started using FPSC when it first came out, even though the minimum system requirements said 512mb.
I am running 3gb now, but only because my other ram chip was flakey, so I pulled it. (I should have 4gb, but 3gb does great)
My video card has 512mb on it, but it uses some system memory too. That card has 1752mb at its disposal.
You can't have too much memory. Like the old saying goes...
"It's better to have it and not need it, than to need it and not have it."
Quote: "I'd add as much RAM as your system (and pocketbook) will allow."
Now, that's good advice.
If the advice is taken, then you should notice the difference right away, and you'll be glad you did it.