Mine is 591 kilobytes and I saved it to a USB stick (which needs to be formatted properly as a FAT32 drive - not NTSF to work).
With your PS3 up and running and USB stick plugged in, outside of GT5 go to your games tab and go to Saved Data Utility (PS3). In there find GT5, and hit the triangle button, then select "copy." If your USB stick is setup as a FAT32 drive you'll see it listed. Select it and it'll copy the files onto the USB stick.
To format the stick as FAT32, do that via your computer (quick format is easiest), and then follow steps above.
Hope that helps!
