Being a Mac user I have not used Bearshare, but have used Phex, and am aware that Limewire seems to produce less search results, than Phex, which tends to connect to many more ultrapeers than Limewire does. I suspect that if Limewire, the largest player in Gnutella, were to make the settings as favourble as other clients, it MIGHT overburden the Network.
Phex also connects mainly to Bearshare UPs, so I'm guessing it produces more Bearshare like results
I tend to use Limewire ordinarily, for ease of use, but I find Phex invaluable for finding rarer files, so allow the two to work for me. Use of Limewire Pro increases conectivity, and if you have a reasonably fast connection speeed and are looking for rare files. I believe Pro would help you. Some would dissagree
In any event, there is only a certain portion of the network that any client can reach, so you will never see all the rusults available.
I hope this helps, it is slight guesswork on my part as I am not a deveoper