Swing Measurements

Mathematically, yes. If you want your pairs of quavers to be played as crotchet-quaver triplets then the setting of 66% is correct (rounding errors excepted). Whether that will give you a "moderate swing" or not is rather less certain.

Here is a forum thread on the topic from last year. Take a look at the New Scientist article I posted there. https://musescore.org/en/node/292457#comment-935648

The moral is: If you want your music to swing, put it in front of a bunch of good swing musicians. Don't expect too much from a computer.

Swing (in Jazz) doesn't necessarily require (exact) triplet length. Some may be shorter and some may give a longer setting; It depends on the artist's feels. Swing is a rhythmic feel.

Once (in my school years) I tested it with a small group (I think there were seven or eight people), the result was a Quintuplet: 3:2; the first eighth takes 3 and the second takes 2.
So 60/40 is the default setting of Musescore, which is a very accurate preset.

Note: Some say this should be the 62/38 golden ratio. It isn't possible for me to make such a precise measurement since there is very little difference.

66% would be triplets indeed, but that's definitely not a "moderate" swing, it's a very exaggerated one. The default of 60% is appropriate at moderate tempos. A somewhat more exaggerate swing can be effective at slower tempos, faster ones normally demand a value of less than 60. But it's all subjective, so go with what sounds good to you, and know that the players reading your score will likely also do what sounds good to them.