Hi,
a tunnel interface is created in software. As such the speed is only limited by
1) the interface speed the tunnel is crossing
2) the encryption throughput of the VPN router.
Depending on your broadband speed and interface requirements a 800, 1800 or 2800 router or a PIX might just be fine.
A table with VPN throughput data for various Cisco routers and firewalls can be found at
http://www.cisco.com/application/pdf/en/us/guest/netsol/ns125/c643/ccmigration_09186a00801f0a72.pdf
This should provide enough information to pick the proper device (you might need a price list in addition 😉
Hope this helps! Please rate all posts.
Regards, Martin