I've noticed that MaxLife gives a SLIGHTLY softer shift. Not mushy, just softer.
I've done 3 pan drain and fills on the Optima this spring. First was MaxLife, which I ran for about 2 weeks (500 miles), and wasn't as impressed with it in the Kia, as I was with it in my old chevy lumina. The next was Eneos SP3 that I got from Napa, and about 500 miles later, I replaced with Kia SP3 that I got from the dealer, at nearly double the cost of the Eneos. The transmission is back to shifting like it used to.
I would agree with the general consensus though; SP3 isn't a very good fluid, as it oxidizes easily. I plan on doing a pan drain and fill once a year in the spring.
Valvoline now has a multi-import full synthetic (not Maxlife) ATF on the market, so I may give that a shot. Apparently MaxLife and Lubeguard Platinum are a good mix too.
Good Luck!