On high mode, the hotspot of my ARC4+ is easily twice as bright as my KL3/M2, at least to the naked eye. This may be due to the fact that my particular KL3 is quite purple, whereas the ARC is much whiter.
Im guessing that what i see is correct, considering as the KL3 is driven at 330mA, with the High mode on the ARC is in the region of 700mA. I guess the only way to be sure is to put them both in an integratig sphere.