An estimate from the following document, vpn_srnd.pdf, says 520 Kbps for the 2621 without the AIM. This is based on 65% CPU utilization, mixed packet sizes with 2 IPSEC/GRE tunnels. I would post the hyperlink, but I cannot remember the URL. If you like, reply to this post and I can email you the copy that I have.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...