I have three BGP upstreams (same provider) in geographically different locations. The biggest pipe is connected to a CCR1036. We switched to it from the 7206 about 7 months ago. We have 500Mbps there and it just ticks along. The other two sites are running older x86 boxes with about 200Mbps each. I'm only taking partial and default routes. We don't have enough upstream diversity to care about full tables. We do have quite a bit of path diversity to the upstream.
If you have the budget, I would run one CCR for BGP. And other CCRs for NAT, queue trees and whatever else. Historically, RouterOS seems to have had issues with one device performing many functions, in our experience anyway. You have probably been doing everything with the 7204.
We have around 3000 access customers, including the DSL.
Our 7206 with NPE-G1 was running about 60% CPU with 140Mbps running through it and handling PPPoE for about 1,000 DSL lines and lengthy ACLs. I didn't want to push my luck when we upgraded to 500Mbps. We kept the 7206 as a DSL aggregation only box.
We see the CCR hit 60 to 70% during a 500Mbps DDoS. Usual CPU utilization is 3 - 5%. The CCR has been up since I loaded 6.12 on it, 136 days ago. It was not that stable on earlier revisions of RouterOS 6. Some of that stability is probably us learning not to try to do too many things on it, some is MikroTik fixing bugs. One CCR with 6.12 or higher may be able to handle everything the 7204 does, other than T1, DS3 or OC3 handling.