Do you think your RAM is under utilized?
Do you think when you copy a big file your hard disk is being grinded, your linux fills RAM and does not allow to run you any useful thing?
Do you think running from live USB or live CD is better than installed system since it utilizes RAM?
Here is a probable solution for running programs from RAM. Install your favorite OS inside virtualbox or VMWare and allocate them 1 to 2 GB RAM. Now even when your harddisk is used by your host OS when copying big files, your guest OS running inside virtualbox or VMWare will continue to be snappy and fast. This is because the RAM dedicated to it can't be reclaimed by your host OS
Does it sound geeky? If not then, congrats, you are there for a treat with your (powerful) computer. Your guest OS running virtually is a probable answer to RAM greed from linux kernel