Performance Street Driven:
Motul Turbolight 4100 10w/40 semi synthetic $45ish

Notice I put this under Performance Street Driven:
Its there for a reason. This oil is actually thinner than say Mobil Syn S 10w40 as Motul is rated at a different temp compared to the Mobil.

This oil should be fine for a daily street driven WRX lightly modified. You run a risk running it on the track, especially in summer here when its 30+ degrees. Grab a heavier weighted oil then.

J