We currently have a 3825 that was used for a T3 connection to the Internet, and the 3825 did a fine job. We have since upgraded the Internet link to a tiered gigabit link, on which we have currently contract for 100Mb. During peak busy periods, we are receiving 80-90Mbps of traffic from the Internet and cpu goes to about 50% processing all this incoming traffic. We will be increasing the bandwidth on the gigabit Internet link, probably to 200 Mb, then 400, and possible up to 1Gb as our Internet demands increase and I'm pretty sure the 3825 won't work for us anymore. What router would be able to handle such high throughput requirements. Other features that we would need to use on the router are nbar, netflow, qos, and very large access lists.
I have this problem too.