Thanks for the response, Michael.
I found busybox about an order of magnitude slower than dhcp-isc. Detecting an array of 100 clients took nearly five minutes with busybox (almost 3 seconds each), while the ISC DHCPD needed only 30 seconds. Is this the expected performance of busybox?
I realize I am using an old version (1.5.1), but it seems like wishful thinking to hope the latest build is 10x faster. (I haven't tested this yet: the latest version won't work with my old distribution, and I don't want to tackle a full dist upgrade unless it's unavoidable -- too many custom drivers and not enough time).
I'm using NoMMU, but I'm not concerned with memory usage -- I have plenty to work with.