I'm on a wireless at home and it's not by choice as the only place for my modem to be placed is right by the doorway of the apartment, my computer is in another room on the other end of the apartment, but the signal strength is excellent, my ping on servers are an average of 30-50 on the servers I play..... I have no other issues with any other games I play, such as RO:Ost, Killing Floor, BF:BC2, TF2, etc.
And I never had this problem until the last patch was installed. Before that, everything was fine. I even have PB running on my BF:BC2 and BF2 & there's never any problems with playing online..... not that I play them often these days, but that's a different story.
My symtoms are much like the description in the original post.
There are no viruses on my system, there are no spyware, as I do regular scans on my system, I make sure my registry is optimized, I installed the Steam cfg files long ago when I was having problems with Ostfront & KF staying on a server for more than 30 seconds..... which apparently had something to do with wireless connections.... and it fixed it.
I re-copied those files again yesterday which made no improvement.
Although the last game I played last night before I went to bed, I had no packet loss or speed hack warnings, my gameplay ran smoothly.... and my ping was higher than normal, of about 45-52..... out of 7 games, the 7th ran fine, though I did have a number of Germans just appear out of nowhere and killing me, while others I was targeting disappeared in front of me..... which I assume was the speed hack thing.