Quick reply...
I don't over-clock. It's out of character of me to take risks which could lead to permanent injury. I am using CSSU-Testing, with extras-devel repository enabled. Sometimes, I install CSSU-devel application (tklock). I do not play computer games... but there are exceptions, such as chess, tic-tac-toe, mahjong... I dislike violence, and I never play video computer games. I am a light developer - HTML, Javascript, CSS, C, C++...
I will use Nokia N900 for as long as I can. I will repair it, replacing damaged parts with new ones, for as long as I am able to.
The only phone I could recommend as newer successor of Nokia N900 is Nokia N950. Maybe, Nokia N9, if you don't need hardware keyboard. But the idea of Aegis makes me uncomfortable.
If I was in a falling air-plane, the objects I would protect would be Nokia phone, Fujitsu computer and identification documents, and yes, in that order. Computer would be turned off and in its bag, so its hard-drive will not be damaged much, even if it is submerged in the salty water (though this possibility is reason enough to consider investing in waterproof-fireproof bag). Nokia would be turned on, and its hardware is much more difficult to replace if any of it gets damaged (yes, a small and waterproof-fireproof-impactproof case for it would be a good idea; but I still would not trust it out of my sight). Identification documents are not that difficult to restore, and hold no sentimental value.
Best wishes.
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Per aspera ad astra...