just another sad story in zfs tuning city

[Randy Bush]

i have a system that should move right along.  but it is as soggy as a
tenugui on an august afternoon.

2*amd64 2.0GHz 4GB 750GB
8.1-STABLE Sun Aug  8 01:05:24 UTC 2010

/dev/mirror/boota                     8.3G    909M    6.7G    12%    /
procfs                                4.1k    4.1k      0B   100%    /proc
tank                                  729G     28k    729G     0%    /tank
tank/data                             729G     31k    729G     0%    /data
tank/data/nfsen                       877G    148G    729G    17%    /data/nfsen
tank/data/rpki                        729G    107M    729G     0%    /data/rpki
tank/usr                              737G    7.7G    729G     1%    /usr
tank/usr/home                         732G    2.6G    729G     0%    /usr/home
tank/usr/usr                          732G    2.6G    729G     0%    /usr/usr
tank/var                              730G    759M    729G     0%    /var
tank/var/log                          730G    415M    729G     0%    /var/log
tank/var/spool                        729G     68M    729G     0%    /var/spool

work0.psg.com:/usr/home/rancid# cat /boot/loader.conf.local
loader_logo=beastie
zfs_load=YES
vm.kmem_size=4G
vfs.zfs.arc_max=64M
vfs.zfs.prefetch_disable=1
geom_mirror_load=YES
kern.maxvnodes=50000

i am tempted to just boot without the zfs memory hacks in loader conf.
any warnings on doing so?  any other clues also gladly accepted.

randy