Supernet block sizes - recommendations?

I recently received a request from one of our sites for a block of 256 network numbers from one of our supernet blocks and have been hesitant to fill it because of the relatively large fraction of the current NIC-allocated maximum lock size (1024 networks) it represents. If I recall correctly, at the Boulder Regional Techs meeting, we talked about "reasonable" block sizes in the 32 to 64 network range. Has anyone thought more about this issue or considered what we should recommend either for the maximum block size to reallocate to our clients or the maximum block size the NIC should allocate to us? --Vince