I've always kinda chuckled when we all get to talking about suspension length and traction bar theory, because virtually no one agrees!
I initially went with the long-ass bars. Then a friend of mine made his truck into a puller and went with the short bars (both are CC/SB Chevies). Both hook equally well, I'd say. We run very similar setups, including tires. So in what amounts to as much as a direct comparison as I can come up with, I'd say the length doesn't appear to be a significant factor.
A year ago I would have argued hard for the long bar, now, what can I say?
I think one of the reasons it might not matter so much is that when you think about it, the purpose of the trac bar is to resist the twisting of the axle housing - that is, you're resisting the torque that the wheels apply to the ground. The body frame and all that absorb that torque (in engineering terms, a moment load) one way or the other. Elsewise, the truck would pull a wheelie and flip over.
Point is, whether you do it with a lot of force on a short lever arm, or less force on a longer one, it's still the same moment load. That's just physics.
What makes the difference? I think it's particular to your truck and how the suspension works together. What works on a Chevy with X chassis length and Y rear spring rate and Z front spring rate may not mean sheet on a Dodge with SFA and totally different spring rates, heavier engine out front, etc.
My best advice, when you buy a truck for pulling, look at what other people with the same exact configuration as you have, and judge for yourself based on their results.
One other thing I'll toss in for you that's directly pertinent to the question you first asked: many clubs over this way are adopting the 27% hitch length rule. If they do that, I think it matters less. The long trucks get essentially penalized by having to run a longer hitch than the RCLB versions. When I did the math, it actually appeared to me that the 27% rule may slightly favor the RCLB trucks, but it ain't by a whole lot. The 60" from center line of the front axle made the hanging weight a more significant lever, as a percent of the total truck length.
So anyway, just keep that in mind when formulating your plans.