My personal opinion is with braid even a 6 ounce will lift immediately. If you combine this with circles when scratching you tend to get stuck a lot less. On a 100m cast with mono. stand with a sinker in your hand held between 2 fingers. Ask someone to strike as hard as possible and see how little it moves. Do the same with braid and see the difference.
I'd cast with a 4 ounce to start as it will pull the braid off more evenly imo. But i generally prefer a heavier sinker, some of my friends cast 3 and 2 ounce on sl20/30 with braid.
If you are going to go that light, i'd go .70 leader, .60 trace and .30 sinker line... fishing with a circle hook you should only need to replace a sinker now and then.
Some go .60 leader, .50 trace and .30 sinker line, i used to but lost 2 nice fish on the .50 trace.