From personal experience and most reviews I've read, there's no visble difference really. MS claims a difference when you use "Readyboost Certified" drives which are basically ridiculously expensive and its a lot cheaper to buy some more RAM lol.
None in ur case. :no:
Readyboost is most effective if u use it basically on a low end machine.
Since u have 4GB RAM, u don't need readyboost. However, if u want to see some marginal benefits, u can use a 8GB stick for readyboost.
The USB stick should be twice the total RAM for optimum performance.
Max limit for ready Boost is 4Gb so this wont help.
In my machine I noticed it made my computer SLOWER to say the least, maybe cause I was using a non ReadyBoost Certified Drive, but it still enabled ReadyBoost.
There is no point in it if you ahve the stated 4GB Ram.