No. Something is going on here. I have the same problem. Had speeds up to 45K. Now, rarely get 5K even with 80 sources. I tried with 4.0.5, with 4.0.6 and even back to the version from last February... still same result.
I've tried tweaking every setting in the preferences, setting all slots to 1, etc.
The only clue I have is I used to be considered an ultra peer, but now it looks like I'm not (ie. I get the little message when I enable monitoring incoming searches saying I won't see much.).
Please someone who knows something, report this problem to someone who knows how to do something about it.

G4, 10.3.4, Cable connection 512/128