If you do a bw test between two servers, their ports are 1gbps each so the test will show 1gbps per direction. Depending on the test and CPU usage while it runs. Are you comparing results with another version of RouterOS or another OS or hardware? Sorry, I mean 1 Gbps test result is total bandwidth...

may I know suspect source of problem ?
is it from my intel pci quad gigabit ? because I tried to do bandwidth test between servers (in 3 of 4 pci port) only get 1 Gbps maximum.

I have tested RouterOS V5Beta3 to my server router with bonding 2 Gigabit ethernet Broadcom for outside traffic (BGP to local internet exchange)) and Intel pci-express with 4 Gigabit ethernet for inside traffic (3 servers). the router stable for 24 hours. but unfortunately incoming and outgoing traf...