There are ram disk softwares the will dump all the ramdisk data to hard drive on sytem shutdown and replace it on startup. This does make shutdown and startup a longer process.
The problem is that 8GB of data will take ages to copy into memory. Lets say that your HD can read at 100MB/sec. That means it'd take over a minute just to copy it all onto the RAM disk. So your "quick loading times" will be offset by that.
I experimented using a RAMdisk for gaming around 9 years ago using a cutdown Quakeworld installation in the hope of getting quicker mapchanges and less lag from demorecording etc. It was a bit of a gimmick really and I soon abandoned the project.

