"Readyboost" has nothing to do with amount or speed of RAM.
It is to do with HDD read/writes. "Readyboost" stores commonly accessed files on to flash drive and if windows can access from flash drive faster than it can from HDD it will do so. A little like a poor mans SSD
EDIT to add,
If you are going to use it "Dedicated" would be the best setting. Please remember modern HDD's are fast enough to beat a USB2 flash drive so only advantage would come if you have USB3 mother board and flash drive.
If a system uses an SSD "Readyboost" is disabled by windows.
Edited by Nervous (Thu 22-Jan-15 12:15:13)