How good is the performance of the hardware AES-NI encryption engine?

I own a DS1813+ and I'm very happy with it, with one exception: Transfer speeds from and to encrypted folders are at best at 1/5th the speed compared to unencrypted folders. The DS1819+ has an AES-NI encryption engine according to its specs, which would be able to do this encryption via hardware instead of using the CPU for it, so I'm interesting in switching to one of these for that feature alone. (The DS1815+ and DS1817+ apparently have this as well, but I want to skip these because of their Atom C2xxx CPUs)

For models with this kind of hardware encryption engine, are the transfer speeds exactly the same for encrypted vs unencrypted folders? Or is there a notable difference? Would be nice to see a bit of a benchmark on this. Thanks!