I'll just say this definitely doesn't agree with my experience, though it's certainly the kind of thing that might differ from person to person, brain to brain.

Here's one thought experiment: imagine variables get longer and longer and longer. Clearly, at some point, they become so long that they're much more unwieldy to work with. Now it's just a question of, as they get shorter, when do the gains start to become insignificant?

(Re QWERTY: Ease of input is certainly a consideration, but hardly an insurmountable problem. We should not forever restrict ourselves to basic latin because that's what happens to be printed on many physical keyboards at this moment.)