Hey TiredFeet...a lot of truth in what you say. How about we quantify it.
Let's suppose you want length L of cord between your hammock end and the tree. L varies by taste. Sneak preview of coming attractions...the longer L is, the more efficient is the UCR relative to the WS.
Let B be the length of the bury. Why you think the bury on the UCR has to be significantly longer than on a WS? I missed those posts. Mine are 10" on both types, and so far have done me just fine.
Bury length of an eye-splice...6" for 7/64" Amsteel, by the book, more or less. Call that S. Let's say the length of the eye is E. 'bout 2" in my riggings.
Figure below marks out where these lengths show up in a WS and a UCR. I'm not counting that a bury length is shorter after the rope goes through, for the lengths of interest that doesn't matter much.
Screen shot 2010-10-11 at 9.46.48 PM.jpg
So to have L feet from one end of the WS to the other you need 2L feet of cord. For a UCR you need L + B + 3*(E+S) feet. The fact that the UCR has one more buried eye than the WS (if you choose to use a bury eye...you could use a knot...)
is where the supposed efficiency of the UCR takes a hit. But that's a fixed cost, and the longer L becomes, that fixed cost is amortized, because the WS length is increasing by a factor of 2 while the UCR system length only by a factor of 1.
I didn't figure tails in because I just tie a stopper knot on those, just to impede slipping into the bury.
Let's do a spreadsheet!
Screen shot 2010-10-11 at 9.50.36 PM.jpg
So according to your scenario of 20' between trees and a 9' ridgeline, you're looking at a value of L---if this was the maximum distance between trees that you'd consider---of 5.5'. 11' of WS compared with a little over 8' of UCR. Yawn. I agree.
But you know, I can hang between trees that are 26 to 28 feet apart, 'cause I'm tall enough to push the tree huggers high. And the weight cost of Dynaglide, I don't mind one bit carrying a suspension with that much cord. That will add 3 or 4 feet of length to the suspension scenario, so we're then comparing almost 20 feet of cord for a WS versus a little over 12 for the UCR. That's a difference worth noting, if only because I have lots of uses for that 8' of Dynaglide other than being on a whoopie sling.
There are other differences, but its all personal taste. Frankly, I'm increasingly drawn back to just using a simple length of cord out to a Marlin spike hitch, then back to an SMC ring on the cord to be tied off. Hang your own hang, choose your own suspension.