[stovt001]

First thing they taught me in high performance driving school is you want to avoid upsetting the balance in a turn. Steering with the throttle is one thing, but the shock of a shift mid-term seems to throw that balance right out the window. If you're racing, rev-match downshift while entering the turn, neutral power or steer with the throttle through the turn, and get back up while going straight.

Edit: Confirmed with my wife, who's actually gone to more driving schools than me (how awesome is that?). She confirmed you don't want to shift in a turn, especially when racing. She was very confused as to why someone would do that.