Mandy: The last mile - the 16 Golden Stairs - should not be underestimated. Plan for 30 to 35 minutes to cover this last mile. I don't know where the name comes from but it is a boulder field. Practice high step-ups or stairclimbing on tired legs.
Also the effect of altitude should not be underestimated. \you need to drink extra to compensate for the thickening of your blood as well as the ridiculously low relative humidity at altitude. Of course too much water without electrolytes can be a problem. A few years back a local and PPA veteran gave me a tip - salt pills. He warned me about cramping after A-frame noting the trail sides get littered with wrecked runners who have seized-up. I picked up a bottle of Hammer Endurolyte capsules at the Colorado Running Co. Took the capsules at regular intervals and no issues.
As for breathing through a straw - can't say I ever tried it. I've got a few gimmicks and gadgets to help me cope with the altitude but nothing replaces the real thing. Given there isn't a lot of time left to the race - try the Altitude Training Mask or Expand-a-lung. Both are resistance trainers for the diaphragm and relatively cheap. Not real altitude simulators but they will get you used to exertion with respiration deficit.
Long story short - you'll make cut off. Just add some spice to you last few work-outs to increase your enjoyment. See you at the start line