hmmm.... I shouldn't put to much stress on the server, it all depends on how many stations you build t once, what are the specs of the DHCP server it may run on?
Basically it's just acting as a file server(as far as I understand) and its like clients downloading anywhere from a gig to 1.5 gigs off the server at a time(unless you customized it to make it bigger or smaller) Mine doesn't even go as a constant stream.
the dhcp server is an old dual P3 1 GHz with 2Gigs of RAM. I'm guessing it should be able to handle the load considering the only one's who will be booting to RIS are the Domain Admins so the load shouldn't get too heavy at one time.