I found a cool trick which will get you pass the firefight at the end of the refinery mission with no sweat.
Ok, so after triggering the refinery meltdown and making your escape, you will get to the last stand off area, where you are waiting for Nicole to bring the car around. At the beginning of this area you will see a box to the right, with a MP5, AK-47, scoped rifle and a shotgun in a briefcase. Proceed up the metal staircase and down the ladder. STOP!
Once you take a couple steps, a dialogue be will triggered. Once Bond says " Nicole where are you? BLAH BLAH BLAH, bring the car around, just get here!" Quickly run back up the ladder and retreat to the box with the stash of guns.
At first I found it difficult to make it up the ladder, so I tried walking backwards to trigger the dialogue and as soon as I heard Bond say "Nicole" I booked it to the staircase and retreated downstairs to the crate of guns. One shot to the back on 007 status, and your dead, but the toughest part is over.
Now just sit back and wait for them to come to you. You can shoot them before the ladder, or when they are climbing up the ladder. I let a couple come down to me so I could get some takedowns, and receiving some focus aim points. I would recommend this tactic, as well as letting a couple get to the top of the ladder for so you can retrieve some extra ammo . I used the pistol and MP5 for guys on the ladder and very close range. Then I switched to the scoped rifle and Ak-47 for guys a bit farther and towards the end of the fight, when the guards take the elevator down on the far left.
There will be a couple guys who will not come after you, so be careful and dispatch them with the focus aim if possible. You should have about two check points so take your time. When Nicole says " I'm almost there!" you should see an icon showing her position at 2000 meters away. Let her come to you and when it's about 90 meters away, take care of any stragglers and the nonchalantly stroll over to the hallway that leads to Nicole.
Remember to take your time throughout the sections and get your checkpoints. Conserve ammo, make shots count. Enemies will not keep spawning at the end and make sure to check your smart-phone for enemies locations when sweeping the area.
Hope this helps and the best of luck to you on your 007 status playthrough.