LS,

What is the fastest way to do relationships? 

In the 6- days we used to create calculated fields where we combined keys from other fields to create a new link field. 
Later on FM7+ came along and we were able to use multiple field in the relationship definition at one, but that was pretty slow compared to the old FM6 version.

Has the speed of the FM7+ version caught up and surpassed the old FM6 version, yet? Especially using large datasets?

Or has a new paradigm emerged in the mean time?

Kinds regards,

Joost

I don’t think there’s a definitive answer about performance comparison with such an old version. I will say that it’s been shown the when defining a multi predicate relationship, setting the first key match to one that limits the child records the most is best practice. 
otherwise, there are so many variables involved in optimization that you’d need to test with a specific file, and deployment.