I am afraid your logic is all wrong. Superfetch is supposed to use up all your memory, and THAT IS A GOOD THING! There is no need to have spare memory as your computer boots. What are you going to do with it? As you use your system, Windows unloads processes from the RAM as necessary (which can be done at 4+ GB/s) and then loads on the necessary processes (which, since they come from the HDD, load at a much slower ~300 MB/s). Unless you use your computer differently EVERY single time you boot (and I mean a different antivirus, firewall, configuration, etc, which no one does), SuperFetch is a win, win, win situation. It puts the files in the memory NOW, letting the commonly used programs run faster right off the bat.
Cheers,
Nick