I'm Lagging the Game?

So, I've been using XBox Live, lately, to rack up points on Halo: Reach (overall, I prefer to play online firefights). Most of the time, it's a pretty good experience with good, solid, stable, speedy servers. Other days... It's occasionally choppy and laggy.

Today, for the most part, it's been pretty good. I had one game where there were four of us playing. Ever so often the game would lock up and one player in the list would be shown as having a bad connection to the server (it was the same player, each time).

A couple games later, I was matched up on a map with just one other person. The game was kinda herky-jerky. The other guy starts whining about how laggy the game is. Starts whining that I'm causing the lagginess and that he's never had a laggy game before. Eventually, the tool quits out (presumably out of frustration). I was able to tell pretty much exactly when he quit - not because the quit notification but because the game pretty much immediately smoothed out.

Here's the deal: I have Verizon's FiOS with the 25/15 package. I'm not hurting for bandwidth. After the game ended, I went to my laptop and pulled up SpeedTest.Net:

So, I'm not getting the full download speed. But I'm getting more than my sold-level of upload bandwidth. In either case, I've got better than 15Mbps in each direction: this is more than enough to support online multi-play on XBox Live. Combine this with the server speeding up after bitchboy-bailed and it seems fairly obvious who the source of the lag was.