Just adding my two cents, I think the Sohal is possibly the meanest out there. I've had a 3" tang stand up to and eventually dominate a handful of other tangs (lt, mac, chocolate, black shoulder, etc) that were 6" +. That sohal is now pushing the same size as the rest, approx 8" and running them all.
One of the absolute toughest and now deadliest for me has been a yellowfin, xanthopterus. I have one around 18" in a 1600g and he punishes everyone. Recently killed two 1' angels, queen and french, and has absolutely been terrorizing a 13" mata. He has also for sure killed a handful of other acanthurus. No hiding space good enough, he is relentless.
Sometimes not sure if natural hiding spaces and lots of room is better, or overstocking the tank and having no territories to establish; the latter is less appealing as a hobbyist but definitely better at preventing fights to the death.