earlier today I've done a small benchmark of the 4220's crypto capabilities (the speed at which you can up/down load when using crypto on the 4220). The results are quite ok for such a small and cheap system.
Upload (to the NAS) was between 3.5MB/s and 4.5MB/s
Download was about 4.70MB/s
It's nothing when comparing it with the unencrypted speeds (10MB/s up and 19MB/s down).