So I should clarify, I am not sure how it compares or how much it benefits the smaller engines. My personal experience and research is primarily for performance vehicles and even more specifically the 5.7 and 6.1/6.4.
The best data I know of, or at least the data that most closely ties to the 5.7/6.4 Jeep, was completed a long time ago over on LXForums.
If you look at the last set of data in the first table you will see a 170 degree thermostat consistently dynoed ~10HP higher than the same setup with a 203 degree.
GIFO3 - Headers, 18" vs 20" & GSM Mod RESULTS
Now this test was not originally intended to be just for the Tstat so you will see a lot of other info there unrelated to this discussion. This is just the best, back to back, direct comparison for these engines.
A quick google search will yield hundreds of articles about the idea in general. Either search for Low Temp Thermostat advantages or for a more technical take, search for engine temperature effects on detonation.
Finally, I think most with an SRT or 5.7L will agree that these machines put out a LOT more in the cooler months. Sure, this is related to intake temps and lower temp coolant doesn't directly affect them, but keeping everything in the engine bay running 20 - 25 degrees cooler, I would think, would help lower all of the ambient air available. Even if running stock air boxes, the air still has to pass through the Throttle body and intake.. Couldn't hurt if those were all a few degrees cooler.
Additionally, having ran low temp Tstats in all my cars since 2005, and being VERY happy with the end Dyno numbers of each, many of them running 10 - 20 HP higher than the same mods (minus Tstat) for others, I came to the conclusion that at the very least, it wasnt hurting anything, and possible, it is helping. (And being a realist, its possible that the barometric pressure or dyno settings were different or I was running better gas or any combination of hundreds of variables.... My own experience isn't scientific by any means)
I admit, it's difficult to determine fact from opinion, and I too may not be correct on my final determination... A lot of my own is circumstantial evidence but between that, the test above and the fact I can find a lot more articles on the pros over the cons, and again, the cheap cost, Its always been one of my first mods.