Post install FWIW

[Quartz]

>When I dd'ed /dev/zero to (re-) initialize the individual
> drives during install, I saw 125-ish MB/s per drive, so this is 90-ish %
> efficient for this write.

Do remember that using dd to estimate disk speeds is tricky since its 
write pattern is somewhat non-standard. You should try a more 'real 
world' test like rsyncing a bunch of random crap with differing sizes.