Quite interesting how you can say that it DEFINETELY is not a lag thing...
I am just making this post to tell you, that the bandwith of your connection is NOT the only thing that affects your lag. Lag is a symptom of bad latency and that is the time it takes a piece of data to get from one end of the connection to the other.
Bandwith or throughput is only about the amount of data you can send at a given time, not about when it arrives.
Think of it as how many trucks you have. Even if you have a thousand trucks, the first peace will arrive when the first truck reaches the destination and not a thousand times faster ;-)
I am no dev so I don't know if this is caused by lag or not, but I read somewhere that this could be the issue and above explanation might suggest that it can be a lag thing if you have a 10 Mb line.
EDIT:
Sorry I actually wanted to post a link for interested people:
http://en.wikipedia.org/wiki/LagThere a also links to latency and bandwith in the article