Without seeing the endresults of each render it is difficult to compare the render engines. Unbiased and biased renders and the enabled features give different results as well.

The firefly render has many differnent options which influence render times greatly such as shadow bias, IDL bounces, reflection/refraction quality settings. Adjusting those could make a much faster render.

The Octane render has 3 different render engines - DirectlLighting, PathTracing and PMC. I assume you have used Pathtracing. DirectLighting is mich faster and gives pretty much the same result as firefly. The PMC render engine is also a bit faster as PathTracing but clears up much quicker with specular surfaces. Using Hotpixel removal and adding a bit of caustic blur will make the render clear up faster as well. It would be interesting to see what the render time is with DirectLighting and hotpizel removal.

I assume that with Vue and Lux there are similar adjustments as well which will make the render faster