Not sure exactly how a chart on these would work, I am curious to see it tho.
Feedneck mounting options is a good suggestion.
The J2L can be combined w/ the S6, they are basically identical aside from milling.
The T2 and the SS-25 will stand out on the chart due to the SS-25's valve body, and pump kit, and the T2's modular design, different grip frames and unique pump.
Parts interchangeability would be nice, could label what internals work in different guns.
Like mentioned, weight and efficiency will be good ones, probably what most people will focus on.
I need a T2 again.......