Efficient vs Elegant design

I'm currently weighing up a variation of designs for the same task, there are two standout designs, let's call them 'Design A' and 'Design B', however they are both quite different.

Design A is efficient in the way that the user would, potentially, be able to complete the task very quickly. However, Design A is slightly cluttered and a bit compressed. It doesn't look as clean in comparison to Design B.

Design B is elegant in the way that completing the task is very clean and a joyful experience. Although, Design B would take a fraction longer than Design A, it is important to note that the difference is quite small. Another point worthy of consideration is that Design B is intuitive but does not use 'standard' interactions, this means it would be a bit harder to learn for some, possibly older, users.

My question is two part:

Is there any available research or guidelines about performance and overall best UX when comparing such design differences (efficiency vs elegance)?

If you were to test these two variations on users, what indications/measurements would you look for?

I have already taken into account what has been given in the answer to this question about efficient vs intuitive. Whilst it was helpful it doesn't take into account elegance nor how to measure these in a user test.