This is perhaps the best overall comparison test on current fly rods that I've seen.  If you are in the market for a 4 weight, or want to understand the differences in rod characteristics before you do buy, then you should definitely check out this non biased, extremely data detailed analysis of this year's rods.  A "well done" to George Anderson at Yellowstone Anglers for this one.

https://www.yellowstoneangler.com/gear-review/2019-4-weight-shootout