Depends on your link speed and how much other stuff you want the box to do. Raw benchmark numbers from the N3150 (first is no AES-NI, second is with):Sorry to be a little off topic here, but how important will AES-NI be if there is only only to be 1 VPN to be used once or twice a day between 2 sites?
type 16 bytes 64 bytes 256 bytes 1024 bytes 8192 bytes
aes-128 cbc 27482.49k 30927.17k 32224.17k 79698.26k 80573.78k
aes-128-cbc 145037.58k 215046.27k 256579.24k 269656.06k 273514.50k
Note that you won't see raw crypto speeds with VPN because of the overhead of other VPN operations--but that gives you some idea of how much more effectively utilized the CPU is, far and away beyond 10% or 50% improvement here or there.