Hi, a little question.
How many firewall entries can RB450G handle without any problems? I mean, it is possible to import for example like 1.000.000.000 IPs and drop all incomming packets from these address?
Thanks for answer.
Sure everything is possible, but don’t expect your routerboard to route stuff faster than ISDN speeds with 1 billion rules 
Assuming all that stuff fits in flash and ram …
At this time, I have a 500 rules fw listing (including, mangle and nat) with no problems on a unique internet gateway.
I could easily reach 1500 rules with more complex scenarios than I have now (adding hotspot facility, ppp’s, more internet gateways, more local areas), but I could not imagine, where a 1b rules could be used to.
I believe that you have reached wrong solution for your problem (if it is a problem and not just a question).
Answering to your question, I cannot answer but there is a limit. CPU (on lots of packets) is the cause of increment on latency. As a result of low resources you will encounter packet loss.
Try to search for iptables limits, since mikrotik firewall is actually that.