I have found game lag to highly variable, with no obvious reason as to the cause. I have had 4v4 games with only slight lag, and 2v2 with some of the same players that have been stop motion battles.
I have a good system so I know that is not the problem. I have just moved house tho and my new connection is borderline crap now, too far from exchange for decent adsl/dsl apparently.
(also discovered yesterday that if you turn the hoover on the internet connection drops out )