Unbound performance issue

Hello, everybody

I have 6-core xeon server with 6 GB RAM, FreeBSD 8.0 and Unbound 1.4.3. compiled with libevent and without threads.
resperf says that max qps for my server is 4500-6000 and I’m afraid this is very low even for default config.

In my optimising attempts I was guided by HOW-TO from unbound.net and some threads from this mail-list and I got the next settings:
interface: 1.1.1.1
outgoing-interface: 2.2.2.2
num-threads: 12
outgoing-range: 7000
outgoing-port-permit: 32768-65000
outgoing-port-avoid: 0-32767
outgoing-port-avoid: 65001-65535
msg-cache-size: 50m
num-queries-per-thread: 7000
msg-cache-slabs: 8
rrset-cache-size: 100m
rrset-cache-slabs: 8
infra-cache-slabs: 8
infra-cache-numhosts: 100000
so-rcvbuf: 4m

Other options are default

And resperf said

  Maximum throughput:   4474.000000 qps

 

It is very low, isn’t it?
If so, where I can find detailed description of every option and its influence on performance?

Thank you in advance.