The rule of thumb for Win95/98 was your static swap = 2X your RAM, but not to exceed ~256MB. So 128MB RAM = 256MB swap file. Unless you get error messages telling you you're running out of VMM, you shouldn't need to increase beyond that, or go back to dynamic sizing.
So for 384MB RAM I would try 256MB first, rather than 768MB, which definitely seems excessive.
It also depends on what apps you run as some page like crazy. Remember also that some programs have their own VMMs, AutoCAD and PhotoShop spring to mind, so you also have to babysit them as well.