Playability factor of 50 is not going to be noticeable or a factor for most players. In fact, Ralph always said it would be difficult to see noticeable performance difference in the Game Improvement categories with differences of 50 to 100 points. That being said, the STi2 is a little different profile, with a slightly wider sole. It could provide a little more playability for you, but only way to know is to compare. The TS1-IM is a fantastic iron that plays well for a broad range of players. It is more of a traditional blade look, but still a Super Game Improvement club. More technology built into it too with the forged high strength steel face on the forged carbon steel body, and the polymer injected inside to provide a great sound and feel.
I think it comes down to the look and confidence that can bring you. If you think you might like the STi2 better, I would try a #7 iron and then compare. A little investment, but worth it (in my opinion), to test before investing in the entire set.
Britt Lindsey