I have 4GB RAM and i had a 4GB USB laying around so i thought I'll give it a try to see how the game performs.
Formatted the USB drive with the exFAT file system with 32768 kb for Allocation unit size.
Used the Dedicate this device for ReadyBoost setting and rebooted (don't forget to turn of USB boot in your BIOS if you have that option).

The performance gains are dramatic on my PC.
Loading outdoors is 90% faster literally.
Loading indoors is just a second.

The best part is that it doesn't matter if you travel to the other end of the world and come back.
Loading times remain the same for the new part of the world and for the old part even if you go back.
Also everything else loads faster and the game behaves much better.

I must say i envy the SSD users when i imagine how much faster the game works on SSD, but for us HDD users i think ReadyBoost USB is the next best thing.
Hope i helped someone with this
Peaze ^^v