Color me confused... what SIZE are these 3pgs or 4pgs pages? HOW OFTEN? (weekly)
I like to be indexed weekly... but most of my pages go a bit slower (bigger than most).
MSNbot/Bing come from many IPs, but most only ask for a dozen pages at a time... not the whole site (my experience)
And on pages that have not been updated a nice 304 is given, not the page...
Have you investigated throttling rapid access?