A 2621, rated at 25k packets-per-second, can do around 800Kbits/sec of 3DES via software encryption. The 2611XM is rated at 20k packets-per-second, so a rough guess is that you'll get 800Kbits/sec or less of 3DES out of it. But this is a simplistic estimate -- the only way to know for sure is to try.