With another hallmark holiday looming, that of course means there's yet another bonus XP event for https://www.trueachievements.com/Gears-of-War-2-xbox-360.htm
Starting today and running until Tuesday 15th, the "Torque Bows of Love" event offers 7x XP on every game mode, and a big 14x XP on Wingman matches.
In Horde mode, wretches become "cupids" firing arrows of love from their Torque Bows. Though exactly how lovely those exploding, fire-tipped, skin-piercing arrows are is pretty subjective.
The XP multiplier should be in effect within the next couple of hours.