The Lucky Gunner test sure is interesting. I tried out a few loads the other day in my K6s and posted my results in the .357 personal defense thread but I think I'll post them again here:
Using my Kimber K6s, I shot some of my .38 Special 130 grain mild reloads, 110 grain Hornady Critical Defense in .38 Special, 110 grain +P Hornady Critical Defense in .38 Special, 135 grain +p Speer short barrel .38 Special and 135 grain Speer short barrel .357 Magnum.
At ten yards, my mild 130 grain loads shot a hair low in the K6s as did both Speer loads. The two Hornady loads shot about four inches lower. The .357 load made more noise and had a bit more recoil but seemed controllable. The Hornady +P also had a bit more bark than the other loads but the recoil didn't seem bad. All of the nickel plated cartridges extracted easily despite having fired many of the .38 loads before the .357s.
At this point, I was thinking that the Speer .357 load might be the best for carry. But then came the shot timer. From the low ready with the shot timer, I shot several strings with my .38 reloads, the Hornady 110 grain +P .38s and the Speer .357 short barrel rounds at five yards. The target was a ten inch plate. As expected, the time to the first shot was about the same for each round. What was revealing was the split times. It took only slightly longer to get the second hit with the Hornady +p as compared to the mild reloads but the split times with .357 were almost 50% slower. I could get about four good hits with the 38+P in the same time as I could get three good hits with the .357 in the Kimber.
For me, follow up shots were almost 50% slower with the .357 load compared to the +p load.