Vorkath speed runner

I need advice for this combat achievement. Is it better to do it on task with rancour and slayer helmet? Or should I do it off task with salve.

I feel like this task is very little skill involved and just requires insane rng. I've tried melee and Kirby method and best I've gotten is 56 seconds. Any advice? Should I keep doing Kirby method or try melee?