Awful FreeBSD 9 block IO performance in KVM

[Dieter BSD]

>>> da0: 3.300MB/s transfers
>>> da0: Command Queueing enabled
>
> root at freebsd:/root # dd if=/dev/zero of=/dev/da1 bs=16384 count=262144
>
> 4294967296 bytes transferred in 615.840721 secs (6974153 bytes/sec)

1) Does a larger block size (bs=1m) help?

2) That's roughly the speed I'd expect without queueing. Is it really
making effective use of queueing, or is something limiting queueing to
one transfer at a time?