Are you only interested in going up through the box or down as well?
Going up through the box, I am to be as smooth as possible. From doing a number of advanced driving + track driving courses, slower is smoother and at speed, better because the car doesn't jerk about as much. Stability is the key here and nothing is worse than watching a car lurch forward on every gear change. I aim to change gear so that the passenger can't feel it but still allowing for me to get sustained and powerful acceleration.
Coming back down through the box, I use rev matching to smooth out the gear change again. This can be achieved by blipping the throttle to match the higher revs as the gear is engaged, or sustaining the revs.
On the track, I generally use the Heel and Toe technique to brake and blip on the down change. In cars like Porsches, it's very easy to lock up the rear diff and spin the car out if you're too aggressive
