Some clarification about the speeds since the TS mixed it all up (by accident I think)...
Speeds are given in Mbits/s, and downloads are normally shown in kiloBytes/sec by the different programs. (Internet explorer/FireFox/Chrome etc). There is in theory 8x difference in them, but with the overhead in mind the general calculation comes to a factor 10. So a 6 Mbit/s connection should give you max about 600 kByte/s. Therefore the 580 kB/s is a very decent speed for a 6Mbit connection.
The upload is in general 10x slower than the download. That is because the majority of the traffic to the internet users consists out of downloads not of uploads... A 6Mbit connection will have a 640kbit connection upstream (upload). A 30Mbit will have a 3Mbit upstream.
My Fibertel 30Mbit connection consistently performs up to standard within Argentina, and depending on the destination outside of Argentina I still get about 20Mbit down. (Funny enough the speed to Europe is better than to the US... All measured using www.speedtest.net ...)
Unfortunately it really depends on where you live.. A friend in microcentro has totally different experiences (a lot slower), and another friend out in the province is very happy if he gets 1.5Mbit via ADSL...