Need a new router ... Suggestions?

Yes, thats about what I'd expect a 1721 to do (actually I'd expect a bit less, around 7-8Mbps).

You don't want a router for what setup you give. You want a firewall.

Routers that are designed to carry 100Mbps traffic are in a whole new class compared to the 1721 (desigend for T1 (1.5Mbps) traffic). A 3825 would probably do what you need, but is $9500 list.

Firewalls are designed to forward at 100Mbps rates (or higher for bigger ones), filter, do VPNs, some IPS functions, etc. etc.

The Cisco PIX/ASAs are certainly capable, but I prefer FortiNet or Netscreen firewall products over the Cisco ones. A F60 or F100A would easily handle what you need with plenty of throughput, and a fraction of the price of a router that can handle it.

Thanks for the suggestions guys. Strangely Cisco came back and told me a 1841 with the HWIC 4ESW would be able to handle the 100 Mbps. I am a bit surprised by this but it is much closer to the cost I have available.

Sometimes people recommend router capacity on the worst case of 64 byte packets.

To handle this you need a pretty meaty router, 3825.

This is the absolute safest thing to do.

On the other hand most actual traffic has a much higher average packet size than this. I recently noticed a Cisco design document that mentioned IMIX traffic distribution and used it to size routers.

An 1841 has a much higher performance that your 1721

I would give it a go if you are using the internet for a bit of browsing, e-mail, etc.if you are offereing a high volume business service or have a large volume of critical e-mails then I would go for something bigger.