Its very simple , if you limite the queries trough gnutella it also means that you limite the results of files ( yes we all know spamm files ) , so if you limite the querie you also forget that those spam files are results and you findout out that you dont even get the results above that 150-300 as you said , we have filters yes but they are just filtering the results so means results that are included in the querie means results to. So the main issue will be the more results the more chance you get to have a decent file above the spam , aswell that rare files show up more decent if you can search with a more wide range query then 150-300.