So I have to say, the experiment in different finishing techniques was (for me at least) fascinating. I also had a suggestion to use steam (thanks Gemmi for the idea) so I wound another length onto the niddy noddy and placed it over a pot of boiling water to steam for a few minutes. (Tip: I used a rack to suspend the whole thing over the pot rather than trying to hold it. Tip #2: Make sure the rack is clean. My yarn smells like banana bread)
This is contender No. 5.
These are samples 1 - 5 from left to right. The most obvious thing is that steaming doesn't cause shrinking the way immersion in hot water does. Curious because the water I used was hot to touch, but not nearly as hot as steam. The steam however did relax the yarn enough to get rid of the twisting.
Here are the five samples showing relative width. Samples three and four were the densest - no real surprise as they were the two that were shocked with the hot and cold water. In sample four, I can clearly see where I had underspun the single as that part of the yarn ballooned.
I'm also intrigued by the way the steamed yarn didn't shrink but relaxed enough to not wind itself back up. I'll have to remember that!