In the real world, the Gimli glider was 9,753.6 m high. How many km can it glide? Quick?
Of course, in real life one would cheat: a nautical mile is about 6,000 feet, so 32,000 feet works out to about 5 nautical miles, which means that it can glide about 60 nautical miles. One can always grab a calculator (or slide rule — they're actually quicker at this than calculators) to be certain (12:1 at 32,000 feet gives 63 nm/110 km).
117,043.2 m. In about 5 seconds in my head. By doing value × 10 + value × 2. Because multiplying by 10 is so easy, because arabic numerals are in base 10.
And by cheating, which obviously we would do as a first approximation, it is also much more trivial in SI units: 9,753.6m is about 10km, × 12 → 120km. At most 1 second to find. Faster again.
But my fundamental point: we already have the mnemonics ready for base 10, and we won't switch away from arabic numerals any time soon, so we might as well benefit from it.
It isn't a competition. After all, the metric system is screwed up: having 60 seconds in a minute is a pain (but wow, so many divisors! — really though, just an inheritance of an ancient culture that did not use base 10 numerals; using higher bases isn't an indication of modernity) and the fundamental definition of the second doesn't map to any physical reality in an intuitive way anymore.
It is simply less screwed up.
Yes, easy halving and quartering was important back when the population was not used to decimals. But surely, most people these day can tell that half of 100 cm is 50 cm, a quarter is 25 cm, and a third 33.33 cm.
So, the Gimli glider had a glide ratio of 12:1. We're 10 km high, how far can we glide? Well, 120 km.
That's how we'd compute it in a metric world. In the real world, the Gimli glider was 32,000 feet high. How many nautical miles can it glide? Quick?