Xara Designer is a 32bit application and cannot make use of all that ram scruff
(See ► http://software.intel.com/en-us/arti...ations-windows)
Until we see a 64bit version of Xara Designer Pro, more than 4Gb of ram on 64bit systems is unuseful to the program.

Also, Xara Designer as it has it's own video routines and relies more heavily on the CPU power rather than impressive video cards (it runs fine on laptops with basic on board graphics chips after all).

What I tend to do when the application starts to chug, is make a bitmap copy of the object that complex object which is slowing down the application, then remove that object.