At this point you can't revise through Sharepoint in ST5 whereas in all pervious versions you could. You need to create the revision using RevMan or when you release the file it will not bump subsequent revisons into Obsolete, just piles them up in Released. GTAC was unaware of this upon...
I would say it depends on what else is eating up memory on your system. We are runnig ST5 with 8gb RAM (Win7 Pro) and it runs great, even on large assemblies. (we are running Win 7 Pro with a litte faster processor though).