Boxboy, he's right. It doesn't matter who has what kind of connect neither of you have an advantage as a result - your lag with respect to any other player is his time to send to the server, plus server processing time , plus your time to send to the server. This is why it makes no difference what kind of connect who has as far as having an "advantage".
For example, let's say you are in the office at HTC and have tapped into their ethernet, and he plays from Taiwan via modem....
If your roundtrip lag to the server is 2 ms, and his is 800 ms, and the server takes 20 ms to process - it will take 1+20+400 (421ms) for a position report to get from you to him - he'll see you on his FE at almost 1/2 second behind where you see yourself on your FE.
But notice - it will take a total of 400+20+1 (421 ms) for a position report to get from him to you, too. On your FE you'll see him exactly the same amount of time behind where he sees himself as he sees you relative to where you see yourself. And when it comes to collisions, all that matters is that your (or his) FE detects your (or his) aircraft touching another object.
(As a side note - this composite lag is where some of the "He killed me from 1200 yards!!!" complaints come from... )
As a further side note, when it comes to the complaints of "deliberately colliding into me!" I've seen one or two players that are obviously trying to time a collision by pulling up hard in front of every aircraft that makes a pass on them - there was one guy who was flying an IL2 who I watched do it 15 to 20 times, as he kept re-upping.
But since you are only guessing as to what kind of lag your opponent has, it's dang near impossible to get it right - if you are a moment too soon, you get a cockpit full of lead - and too late, and you'll collide on YOUR FE instead. It's pretty much impossible to game with enough success to matter, and once you've twigged that a player might be going to try, they are handing you a freebie kill. It only has even a remote chance if you aren't expecting it.