It won't go faster than the initial speed you set TACC to.
eg.
1. Turn TACC on at 60. Go to 40 zone, it will reduce to 40. Go back to 60 zone, it will go to 60. Go into 80 zone, it will stay at 60.
2. Turn TACC on at 80. Go to 60 zone, it will reduce to 60. Go back to 80 zone, it will go to 80...