400 msl and -40F is nearly -7000 ft DA.
Not really--assuming 30.00 altimeter, it's -871' DA. At 31.00, it's -2108' DA (electronic e6b). Still darned low.
Edit: an online DA calculator claims -6991 DA at 30.00 and -8172 DA at 31.00. One of these electronic marvels is wrong!I was so accustomed to just leaving the throttle alone after learning how to work a CS prop in Laramie that I was totally surprised to see how high the MP goes on take off from low elevation airports. But it's not a big deal to dial it back to the top of the green before dialing back the prop. Just keep flying the airplane at the same time.

I think that's the gravamen of Mike Busch's article, that it's a lot more critical to keep control than to worry excessively about reducing the MP right away.
But turbo'd airplanes, especially ones with manual wastegates or fixed wastegates, are much more sensitive to over-pressures. There's a big difference between showing 31" on the MP or showing 40" or more in an engine designed for no more than a couple inches over 31".
Cary