The nfs server on openbsd has been super slow.  I thought it was the result of wifi + an old computer until I tried an scp download.  the difference was several orders of magnitude.  Anyway, the solution was to cut down the size of the data packets used by the protocol.

Here's my /etc/fstab - the change is in bold.  Apparently there's a sweet spot of not-too-small and not-too-big.  These sizes are measured in bytes, by the way.  That's a packet size of 4 kb that I'm specifying.
one:/home/admin/storage     /storage  nfs  rsize=4096,wsize=4096  0 0