ASR vs 7604 for BGP border router?

What kind of budget do you have? I think it really depends on what you're going after.

Both would work... Is there something specific you want to do? Honestly, your current bandwidth utilization and need could be handled by an OpenBSD system.

I think I may be missing your exact question. Are you asking which would work best? Or simply asking about reliability?

In my opinion, I prefer the Juniper MX series over the ASR. However, there are plenty of fanboys for ASR's. I really don't think you could go wrong either way.

Unless a deciding factor is budget or something along those lines...