I think I'm experiencing some kind of glith with these challenges. I've gotten 15+ and 20+ killstreaks, but still don't have those medals unlocked. the same goes for the Quad Feed one. I got a uninterrupted quinn in the killfeed with a LIghtning Strike today and nothing.
Quoth The Raven Nevermore http://www.last.fm/user/Liquid_Exodus
You can't get a quad feed using only a killstreak. It won't count unless they're gun kills. Same goes for things like Relentless, Brutal, etc. Non-killstreak kills only.
EDIT: if you're really trying for the killer challenges, I'd strongly suggest using the intel-based streaks. Things like UAV/CUAV/VSAT/EMP will give you a leg up while also denying your enemy intel and helping to keep your gun streak alive. Good luck!
GT: N7 Honor. CAUTION: Above post may contain opinions.