Well, I've gotten gold on the Warehouse in Blood Harvest at 10:11. Here's how we did it:
Hunter rifle is useless on this level, either autoshotty or assault rifle, though I prefer the autoshotty and I think it's the better weapon for this level. Grab gas cans, each of you, as well as molotovs. Close the back door and open the door that triggers the event and go through it and up the stairs. From there, the zombies will come in three directions, assuming that you are upstairs and facing the alarm door room:
1. the room itself
2. the somewhat blocked room halfway up the stairs
3. to your right on the upper level
Basically, start by using pistols only and use your primary weapon when feeling pressured. Start throwing gas cans one by one into the alarm door room doorway or room and set it on fire. Deal with tanks when they come. Smokers and hunters are no threat since they can't smoker you off the upper level due to the railings (they don't break) and the hunters can't jump up there except by going through the staircase, which one or more people should be guarding. Once the gas cans are gone, start throwing molotovs into the alarm door room. Don't waste them on the tank, since they have normal level health. Then once all molotovs and gas cans, and the extra gas cans lying around have been exhausted, fall back deeper into the upper level. Infected will come two ways: the staircase all the way to the right, or to your left. Pistols are a must because the ammo cache is too far away.
Leastwise that's how we got gold on this level.
As for the Terminal on Dead Air, the bathroom is probably your best bet. We could've gotten a way higher time, but I fucked up in grabbing another grenade and got fucked over during a grace period. (Thought I grabbed it, but didn't, tried again, got pounced, and the rest follows.) Autoshotties are your friend on this level. Will retry this soon, since our time was 5:32 or something like that.
As for Last Stand, we've tried many places, but it's fucking hard since walls break around you. We tried a corner in the house itself where the kitchen cabinets were. Stockpiled gas cans and held out there, getting 4:52 as our best time. I've seen a friend get 6:16 I think, and I haven't encountered anyone getting silver or gold on Last Stand.
As for the Gas Station on No Mercy, I believe I got 6:26. Went up the lift into the room. Held out there, and then moved lower. I have yet to find a solid strategy for this level once we get into the room and when to move lower, and the garage is a no go since the tank can easily incapacitate the survivors by coming in from the side and throwing the car.
@LX925: what's your steam ID? Mine is Islidox