How much RAM does your current machine have, Jon?
When you are running a 32bit application in a 64bit operating system, the 32bit app can have up to 4GB of physical RAM if it has been programmed to take advantage of it (which I believe the synther has, based on the output of its log files). If your computer only has 4GB of physical RAM, however, then some of this will be under use by the operating system, system services, and any other open applications. I think that you probably need a machine with at least 6GB of RAM before you can claim that you've exhausted the limits of the 32bit synther.
When you are running a 64bit application in a 64bit operating system, the 64bit app can have up to 8TB of physical RAM, however the largest amount of RAM that I have heard of Microsoft or id Software installing is 192GB of RAM, so it will be a few more years before anyone exhausts the limits of 64bit computing.