So for those who have the hardware to use 3 consoles, and have access to 3 gold accounts (or 2 via Home Console trick), I found a way that may be twice as fast.
Using 3 consoles, I had access to 5 players.
Console 1; secondary account from the Shared gold, 1 player, host of the lobby.
Console 2; secondary gold account, 2 players split-screen.
Console 3; main account going for the achievement, 2 players split-screen.
Using the account that's not split-screen, I created a CTF lobby in multiplayer, obviously a player match, not ranked;
Capture the Flag
Map: Facing Worlds
Maximum players doesn't matter
Bots Disabled
Goal Score: 1
Time Limit: 10
Force Respawn: Yes
For mutators I used Speed Freak, Instagib and Low grav.
once the lobby is up, join with the other secondary account with 2 players, then join with your main account. That should automatically put you in the 2 players team.
Just run to the enemy spawn, press X to use the translocator, with low grav, it basically flies across the map lol.
go behind the enemy base and stand opposite the enemies, and murder the 3 enemies over and over. Should take 5 minutes.
Once over 200, capture the flag to end the game, I didn't wait for the next match to start, I just pressed Y, went to menu, waited for the "Save" icon, then quit the game out completely.
Then change the time using the trick from the other guides, reboot the game, sign in your guest again and just do quick match to rejoin your still-running lobby.
You cut on lobby creation time and kill times. Took me about 4-5 hours.