>>No idea if this is still appropriate today, but back when Mac Rubel did lots of experimentation on this stuff, he found that about 1/3 of physical memory worked best.
Mac Rubel... whatever happened to him?
I seem to recall his(?) advice that there was little benefit beyond about 64MB. Of course those were the days when large strings were to be avoided and x86 Windows couldn't address more than about 3GB RAM so the 1/3 rule never risked approaching the allowed 2GB...
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1