A few things to keep in mind,
Using the bandwidth limiter in winmx will cost you some bandwith to overhead, close to 1 Kb/s per down-/upload.
If you have downloads running some outgoing bandwidth is needed to maintain the downloads.
To obtain the best download speed the best value to limit your outgoing bandwith at is in general about 70% of you maximum outgoing bandwith.
If you have no active downloads, disable (untick) the upload limiter to give maximum uploadspeed.