I get decent marks and don't have cast iron. I'd guess that CI will work better because it likely retains it's heat better.
All I do is get a raging hot arse fire, place meat on hot grate (listen for the "SSSssssssss", LEAVE IT ALONE, turn 45 degrees, LEAVE IT....flip and repeat. Because I don't have CI, when I DO move the meat, I try and put it on a different section of the grate (one that's HOT).
18.5", 22.5" OTS
Large BGE (chambersuac's)
The Fiery Furnace (chambersuac's)
Big JT's Smokin' BBQ Competition Team