IActionResult or async Task<IActionResult> what are the advantages?

Question

We're going to create a new API in dotnet core 2.1, this Web API will be a high traffic/transactions like 10,000 per minute or higher. I usually create my API like below.

[HttpGet("some")]
public IActionResult SomeTask(int id)
{
   var result = _repository.GetData(id)
   return Ok(result);
}

If we implement our Web API like below, what would be the beneficial?

[HttpGet("some")]
public async Task<IActionResult> SomeTask(int id)
{
    await result = _repository.GetData(id);
    return Ok(result);
}

We're also going to use the EF core for this new API, should we use the EF async as well if we do the async Task