You will have to forgive me if I feel very strongly on this issue. This is because I had to abandon my car in deep snow when I was young and received frost bite injurious trying to find shelter.
All season tires are rated for mild to moderate snow . Here is an excerpt from tire rack. “ If you live at the edge of the snowbelt and infrequently get snow you may want to select an all-season tire.”
I know that in general you can “get by “ with all season tires in snow , However the comment “Winter tires are overkill” is a huge jump in logic and should be ignored by anyone from deep snow
I have driven Subaru’s in snow for over ten years and they do exceptionally well. There is no reason why the STI should not do well. But be aware of the following. Around here the most common car to be found stuck along the sides of the roads are SUV’s and 4 wheel drive vehicles. This is because they tend to be over confident and drive to fast.