Great test, thanks for sharing.
It looks like you used a full house .357 and an anemic .38. If you had used a +P 38 the times would have been even closer. If you have the time and inclination, try the test again but this time use a smaller target area like the circle on a F.A.S.T. target. Resolve to keep your shots inside the circle. You can print up a FAST target using 8.5 x 11" paper. Then try it one handed.
Just to reveal where I am on the matter...my views on 'stopping power' have me preferring to use a quality 38+P like the 135gr +P Gold Dot over a .357 load.