Capacity relates to contamination input. You could have a filter with 5 grams of capacity but if your engine only generated 3 grams in the FCI, you are still golden. If you have a good, tight, efficient air filtration system and a modern engine that doesn't shed much metal, contamination inputs are low and almost any filter can go 10K in terms of capacity. I just finished a 15K run on a P1, for example.
A statistic I got from a filter engineer was that the average filter in the average car at the average OCI/FCI is less than 50% loaded when removed. Doesn't apply to everyone, of course, but i you have your inputs under control (mainly a good air filter) then you should fit at or below that average.
Also, when looking at capacities, pay attention to part numbers. The spec you see may not apply to all part numbers. If the example is a large fitler, say the common FL1A equivalent for a big Ford engine, it's going to have a great capacity than than the little filter for a Honda. A "coffehaulic" mug vs a formal teacup. IN the case of the Puro examples, I believe they are both the same application, so the 27 to 13 gram comparison is accurate.
An advantage to a higher capacity fitler is the avoidance of bypass as you near the end of the FCI. If your engine typically generated enough to load the OE capacity filter to 60 percent, on a cold start that amount restriction could cause the filter to go into bypass more easily/often. With more capacity (either from more filter media or a better media), with the same amount of contaminant loading, differential pressure is lower and the filter is less likely to bypass.
