The data sheet (http://www.cisco.com/warp/public/cc/pd/rt/2600/prodlit/kaos_ds.pdf) indicates that throughput on a 3745 using an AIM-VPN/HPII is up to 180 Mbps for 3DES or AES-128 algorithms. On a 3800 series it should equal or exceed that number. I recommend you consult your account SE for acces to Cisco internal information that might give you more definitive numbers for yor application. I seem to remember that Cisco was moving to hardware optimization to include AES-256.
Hope this helps, please rate helpful posts.
