Size depends on what your going to primarily do with it. I have a 72" EA on a K6060. I primarily move 12' to 16' logs that are between 8" and 36" round. I move all the slash that comes off them as well. I can, after much practice, pick up slash piles and leave a rake clean surface. It definitely takes practice though. When I first got the grapple I was very frustrated with the ability to pick up slash and wondered if I had mad a mistake with this grapple. Then I watched a professional logging crew do it with a 96" on a big bobcat. Its a technique thing, and man this guy was good at it. I watched for about an hour and then went home and practiced...a lot.
The wide grapple also makes root raking faster. For me, and what I do with it, I couldn't see a smaller grapple being as useful.
I can pick up a single <1" stick with mine, again practice and challenges from my 11 year old son. The teeth on the EA line up very nicely, but only at four points.
From a build quality perspective, I am totally satisfied, I abuse the crap out of this grapple and have never tweaked it. Our neighbor bought a "cheaper" grapple that he has had to fix twice. Two bent tines and a busted weld, and his isn't as big as mine. The only issue, and its really a nitpic, I have with mine is the angle of the grease zerts on the rams at the fixed end. Kind of a pain to get any grease gun on. Not EAs fault, its how the holes were drilled in the rams at the ram manufacturer.
I also ran this grapple on my older K4060, but it probably put to much stress on the arms if you picked something big up that was not centered. Didn't bend or tweak anything but you could definitely see it load the arms up unevenly. I would have to put it down and pick it up more towards the CG. The K6060 arms don't flex at all.
Hope that helps from someone who cuts and moves 15-20 big logs a weekend.