I have used a restrictor plate before. It was not the ticket for me. It takes away from driving the finish line with the throttle. You lose a ton of throttle response down track.

a manual adjustable stop is the way to go in most cases, although some rules say you cant use those. In that case an adjustable throttle cable is the ticket. The throttle cable is what I use. I have used it to run open comp and slow down to 7.0 also. ( my car runs 6.20s and 30s ) A good cable bracket like the Jegs brand one is easy to mark and measure for adjustments between rounds.