jsperf for js objects vs array tuples
You should consider testing only the creation of the object/array, i.e. [ x, y ] vs. { x: x, y: y }, and also how it reacts to more items:

http://jsperf.com/array-vs-object-tuple

I'd say that the conclusion would be that there is no dramatic performance difference, and they both react reasonably to an increased number of items. Either is cheap enough that the actual performance of the code is usually decided by the actual work of getting the values to put in the object/array.

So, you should normally use the one that makes for conventient use of the result, and maintainable code. Having the ability to name the items in the result can definitely be convenient if you have more than just a few.