Note that having lots of virtual memory can help open larger documents as well. It can be a bit convoluted to set up...
(On Windows, open Control Panel. Select 'System', Go to the 'Advanced' tab, in the Performance frame click the 'Settings' button, in the Performance Options pane click the 'Advanced' tab, down at the Virtual Memory frame check you have at least 2048 MB or virtual memory. Click the 'Change' button if you need to. From the Virtual Memory panel, select a drive where you have lots of space, click custom size, type 2048 in the 'initial' setting, and 4096 in the maximum. Click the 'Set' button, then click 'Ok', click 'Ok', click 'Ok', and close the Control Panel)
Blimey. That's a LOT of steps!
I'm not certain about OSX - anybody?
Really, just adding more physical memory is the best way to improve performance if you want to work on bigger documents. RAM is cheap.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"