What does more damage is going into Cat Form and doing another Shred. You should be shifting instantly with a macro between energy ticks.
By delaying your Cat Form, you’re wasting your energy regen and defeating the purpose of power shifting. Also, attacking out of form triggers the swing timer for your weapon rather than the 1.0 speed of your Cat Form’s attack. You’re also not benefiting from the Cat Form attack power increase, or any of your Feral talents.