1. No. Cockers all have the same basis of parts, thus all are all the same. Only the oddballs are different.
2. Breech wear is determined by the bolt material, and the fit.
3.that depends on the parts used. Using lower quality parts that don't have a good fit, will effect the ahot will have.
4.el efficiency is determined by the spring combo (valve & hammer spring), which provides a mechanical dwell, the valve and the bolt. Limiting the restrictions of flow, having good paint to barrel match and all the normal things. Things like sweet spotting the regs, and using the IVG (spring tension adjuster) to change velocities, all help turn a cocker based gun into a very efficient gun.
5. If a cocker follows the same design, but different parts or 0lacement, it is still an auto-cocking pump. That is the basis of it, a self automating pump gun. The sear lug, determines where the hammer is released on the trigger pull, the 4-way switch point is also determined by the trigger point. As i said before, they are a Rube Goldberg machine, ovey complex, but has a mystical attraction. There is a balance of where the parts live & work together but when that balance is upset by either not understanding the symmetry of part interactions, swapping in parts, or the stupidity of the player changing the parts without understanding the 2 former points.
In a modern ressurection, it is simplified and a lot of the mysticism has been removed. To a point, you set it up, and only slight changes to the LPR are ever needed.
6. A full body ID FLE weights much less than some half blocks (i assume). Weight and feel are all personal and subjective. Because of at least ID bodied guns, most of the extra meat on there has been removed. But, the biggest factor is also the parts that make up the gun. Stainless parts, brass parts, the regs, the barrels, all those parts really throw in variables that effect the weight. So go with what looks the best.
I am admittedly an amateur on cockers, no expert. I hope that more people respond to this as cockers can and will be very personal and opinionated.