I tested RB333 with RouterOS 3.0rc3. eth1 and eth2 setup bridge mode with 64k packet size.
setup bridge use-ip-firewall = no
throughput = 37.1kpps
setup bridge use-ip-firewall = yes
throughput = 14.3kpps
maybe enable NAT throughput will be lower!!
How to improve throughput???
I got a heart attack first time when I read it!!!
Don’t do that again!
Clarification:
kpps = thousand packet per second
Configuration:
only system, advanced-tools, routerboard package enabled
/ip firewall connection tracing disabled
/interface bridge settings use-ip-firewall=no
/ip neighbor discovery disabled
Our results are:
bridging: 81700 pps = 81,7 kpps
routing: 41000 pps = 41 kpps
also make sure the packets (test) is generated by a powerful machine, not every PC can generate so many packets
So what about enable NAT rule?
NAT will require to enable connection tracking - so it will be slower
I think RB532 RB33 and the same performance
no way. tests indicate that RB333 is ~ 2-3 times faster than RB532
rb333 test NAT when the packet size is 64 bit
throughput only 15kpps
i thinks is too slow
my test is 81000pps, on same conditions. so your test is bad 
Normis:
Does Miktrotik have throughput performance measurements for each of its routerboards with different packet sizes? It would be nice to have a table so everyone can reference it (obvioulsy caveated with lab and test scenario information).
yes we do. we might publish it in near future. an old one actually is already on the routerboard site:
http://routerboard.com/pdf/results_18may2007.pdf