I do so much work with the Geth Engineer...it really isn't even fair lol.
I get tons of kills and assists, so my points just keep on rackin' up.
Most of the Bronze missions are about 15-22 minutes I think. I've beat Silver a few times, and haven't even tried Gold yet. I feel like to play Gold, I would need to be on a squad where everyone is at least a level 18, and has full missiles, medi-gel, ammo packs and ops packs. Everyone would have to communicate and call out who is using a missile on a certain enemy and keep everyone informed on your medi-gel status. I haven't ran across many people with which I think could get through Gold.