Well, I managed to squeeze in a couple nights of Gears lately. Been doing Dance Central 3 and Borderlands 2 mostly. Got 2 more Onyx Medals tonight: Old Schooler and Lancer. All I need now are Retro Lancer, Gnasher Shotgun, and Heavy Weapons and I'm finally done.
Heavy Weapons probably shouldn't take too long. As for the other 2, I have about 2900 gnasher kills and 3600 retro lancer kills to go.