QUAKE 4

Seasoned Warrior - Played over 5000 ranked matches.

This is the most time consuming achievement in this game. The quickest way to get games played is, Quickie Tourneys. It takes only two kills to end the game.

The other fast way to get games played is getting 8 people together, which will get rid of the two minute counter before each match. After 8 people join the lobby the game will start. Deathmatch quickies have a 5 kill limit.

Seasoned Warrior - Played over 5000 ranked matches.

This is by far the most time consuming achievement in the game.

The above guide is a good solution but if you have 8 players in a lobby, it will cause an xboxlive error which usually happens every 5-7 games. When this happens all 8 players will have to go to the xbox dashbord and re-boot the game. Because if you dont then every match you play after that will no upload to the leaderbord.

If you happen to have 2 Xboxes and 2 copys of quake 4, then you can search with your main account then search with your second account on any game type. It will take 2 min to get in a game, but when you get into the game you can just quit out with your second account. And that will give you a win and a game played, total time per game with loading time approx 2.30-3.00, and from my experience i have yet to get an error. If a random should happen to jump into your lobby then dashbord both xboxes, because that may cause an xbox live error to happen.

Play over 5,000 Ranked Multiplayer Matches.

I got tired of micromanaging 8-man sessions very quickly. I found that we encountered tons of Xbox Live errors, which prevented stats from properly recording. I also found that managing logistics for 7 other people, both before and during sessions, was incredibly stressful. The amount of time saved by eliminating the 2-minute countdown timer was easily lost just from the clumsy nature of the sessions. Luckily, there's another effective way of doing it that's easy, almost error-free, and requires very little attention.

1v1 Quickie Tourneys
This method is mindless, simple, and ultimately almost as effective as using 8 people. A single round of a Tourney only requires 2 players to start and 2 kills to finish, which makes them far superior to Deathmatches or CTFs. You simply need to set up Ranked Quickie Tourney matches with 1 other person (or a second box). There are a small handful of levels, each being pretty small. All you have to do is pick a spot on each map to meet your partner and have them kill you (or vice versa) twice. DO NOT bring a 3rd player into the mix, as it will add multiple rounds to each Tourney match; they are tournaments, after all. You'll want both players to dashboard every 20-30 minutes, to be safe. If you don't, you may start to run into the problem of having stats not properly record. Also, if you receive the dreaded "Xbox Live Has Encountered An Error" message, you will both have to dashboard as well. These are the perfect type of sessions for watching movies or starting a new series on Netflix, Amazon, or Hulu and just zoning out. It requires very little concentration. Depending on how fast you are, you will hit anywhere from 18-30 games played in a 2 hour session. Slow, but that's Quake 4 for ya.

If you do manage to get 8 people then quickie arena ctf matches can be faster than dm's. 2 captures and "YOU WIN" (or lose, but that doesn't matter). This is good if your teamates have a tendency to get trigger happy.

Just adding to the latter part of Vito084's solution. If you have two xboxes you can indeed quit out the guest however if the guest gets host then you cannot do this because you just lose connection to the game and it won't count. However I discovered some weird work around. When doing this, just make sure the Gamertag of the account you're quitting out is after your main account's gamertag alphabetically.

For example, my Gamertag is XxFrAsZeRxX, so I made my dummy account's gamertag start with a 'Z'.

For whatever reason, doing this ensures your main account (the one earlier in the alphabet) will ALWAYS get host, so your dummy account can quit out every time without any problems. I've ran 766 games so far and never had a game not count.

One additional note: Doing the quit method like this prevents Xbox LIVE errors, so you will never have to dashboard. I ran 129 games in one sitting and never had to dashboard once. So this is by far the best method if you can't get a full group of 8.

EDIT: It appears the way your network is setup dictates whether or not this method works. I'm not sure of the exact settings though. I switched over to a new router part way through the grind and this stopped working 100% of the time (it was more like 75/25 towards the end). I'll do some experimentation to see if I can get it to work.

If you have 4 xboxs there is a trick you can do to get matches done in 2.5 minutes or even as low as 2 minutes. Lets say you have accounts 1,2,3 and 4. And lets say account 1 is the main account that needs the achievement. So what you can do is first search with accounts 1 and 2. Then as soon as the 2 minute timer is up, have accounts 3 and 4 start searching and let that timer go. Then play the match with accounts 1 and 2 while accounts 3 and 4 are in their own lobby. Then when the match end between account 1 and 2, account 1 searches and finds the lobby of account 3 and 4 with probably 30 seconds or less on the timer. Then account 4 backs out and leaves account 3 and 1 in the lobby. Then accounts 2 and 4 make their own lobby and start another 2 minute timer. You can do this trick to reduce the timer down to 30 seconds as oppose to 2 minutes.