By default V-ray Reinhard Colour Mapping is set like this:
When set above the total render time was 10min08sec on i7-4900MQ 4 core CPU laptop the rest following Solidrocks Good settings using irradiance map and light cache.
With the Clamp output ticked and set to 1.0 then the render time was reduced to just 4minutes 58 seconds. The image looks identical.
With Burn Value set to 0.75 then the rendering time reduces to 4 minutes 20seconds.
But brighter parts of the image are duller with the Burn Value put to 0.75:
The difference when turning subpixel mapping on or off is shown in the video below. The highlights become slightly pixelated and have less detail and are more blown out: