Rob,
I suspect it's more a software limitation than Ram, and i mean that in, for example. Logic being limited to 3.7GB. If Logic could address 80 or 90% of installed Ram, then we'd all be loading 16GB or so, and having a reasonable time of it.
And in addition, if the Ram required wasn't dependent on Logic, i.e. All VI's and presample loads were handled external of the program, then 4 x G5, 16GB= 64GB, 50 usable, you get the drift. The fact remains though, Logic won't address anymore than 4, and software companies who develop for this platform will always have to keep that in mind. Standalone software is ok, but it would be a lot simpler to load the lot into one program and go play. That's why we have 'Ramplimise', and a zillions comments from every forum about limits and overloads on machines. As i understand it, Kontakt takes anything up to half a gig, and Gigapulse will only play with 2 or 3GB, so there's a general shortfall across the audio board. The day a developer gets their act together and builds a great DAW with no built in limits, is the day Cubase, Logic, and the others will get the push.
But who knows? Maybe one of them will wake up in time?
Regards,
Alex.