Hi Phil,
...if you do the math, you used 68 cu. ft. of air.........and if she ran her tank totally empty then she used 80 cu. ft. of air, which is only about a 15% difference in air consumption between the two of you. If she's a new diver, with more experience it won't be long before she matches, then exceeds you in air efficiency, since she's already pretty close to you now.
For the short term, swapping tanks is the obvious answer, as your 100 cu ft tank has 25% more air @ 3442 psi than her 80 cu. ft. tank, and since she's only using 15% more air than you, you'll be the one running out of air first.......or if you only fill the 100 tank to 3000 psi, that provides 87 cu. ft. of air, giving her 9% more air than her 80 cu ft. tank, and since she's using 15% more air than you, she will run out just slightly before you do.........or if you fill her 100 cu. ft. tank to 3200 psi, that gives her 93 cu. ft. of air, which would pretty much exactly match your endurance with the 80 cu. ft. tank, as that's 15% more air.
...as to the other issue of what's stamped on the 1st stage, I'm assuming the 3000 psi is stamped on the yoke......I wouldn't worry about using the Micra 1st stage on a 3400 psi tank......last summer in Cozumel Liquid Blue Divers provided us PST HP 120 steels, and everyone used yoke 1st stages without a second thought......especially since by the time we'd gear up the tanks had long since cooled to 3200 psi or so........no problems whatsoever. I'd just make sure the O-ring on the valve face is in good shape, and giving a good seal....that's a much more likely failure point than the risk of breaking the actual 1st stage yoke.
This past summer I spent a week in Bonaire, and a week on JULIET in the Bahamas, as well as a Labor Day weekend at the Texas Flower Gardens, on all 3 trips we used AL 80's...and all the fills ranged from 3100--3300 psi, everyone used yoke 1st stages without incident........the only 'issue' would be the occasional worn-out yoke O-ring leaking, as expected on well used rental tanks, I always have those in my save-a-dive kit and switch them out as I deem necessary.
Karl
