We tested doPDF with 30000 pages in here and it doesn't crash. Furthermore, during the actual conversion to PDF, dopdf (process will be listed as dopdfcl6.exe) occupies only around 1Mb of memory. However, the program you're printing from might need memory and CPU in order to complete the printing - for instance during a test of printing 8000 pages from Microsoft Word 2007, the memory occupied by Word went up to almost 1GB during the printing, while CPU was close to 25% (on a quad-core Intel CPU @2.67Ghz). You can test that by yourself using the Task Manager.
So I'd recommend splitting your large documents in several other smaller ones, or try printing from a very powerful computer.