[Tor-BSD] Performance loss migrating Linux -> FreeBSD

[failure]

Hello,

to add some diversity (and learn some new stuff) I migrated my VIA Nano
U2250 1.6Ghz (no hw accel. for encryption) powered dedicated exit node
from Linux to FreeBSD.
The throughput limit is the CPU which was able to push around 82 Mbit/s
max with linux but is only able to push 67 Mbit/s max with FreeBSD.
Memory usage is much lower on FreeBSD.

Linux was: Ubuntu, 4.3 kernel, haveged, postfix, ntp, munin-node,
IPtables rules (as suggested by torservers.net[1])

FreeBSD 10.3, std kernel, munin-node, sendmail, ntp, pf

pf.conf:

set skip on lo
set optimization aggressive
set limit states 13000
set block-policy drop
scrub on em0 reassemble tcp no-df random-id
antispoof for em0
block in proto tcp
block in proto icmp
pass in on em0 proto tcp from any to [IP-of-exit] port 443
pass in on em0 proto tcp from any to [IP-of-exit] port 80
pass in on em0 proto tcp from any to [IP-of-exit] port [SSH-port]
pass in on em0 proto tcp from [IP-of-munin-server] to [IP-of-exit] port 4949
pass in inet proto icmp all icmp-type echoreq
pass out all

sysctl.conf:

net.inet.ip.random_id=1
net.inet.ip.portrange.reservedhigh=0
net.inet.tcp.blackhole=2
net.inet.udp.blackhole=1

Would migrating from openssl to libressl maybe improve things? Are there
any other things I might have missed or is there nothing to do about? A
18 % loss of network max speed (which correlates to the loss of the
average speed) seems to be a lot for me.

Thanks for any help!

[1] https://www.torservers.net/wiki/setup/server