The absolute best approach is to perform reads on specific dn's eliminating the need for filters altogether, but of course you need to know the dn's.
I do know the specific dn's .. but I found that doing say 6000 separate calls is far more expensive then (in my case as I can't do more then 750 at a time) 7 calls with 750 each.
http://www.mentata.com/ds/retrieve/congress/housevote/VC107H21
Jon Roberts www.mentata.com