I found something interesting today with the HDMI and HD-SDI outputs on a Scarlet-X. There is a pretty drastic difference between the luminance and color coming out of each of them. The HDMI is warmer, more contrasty and slightly darker than the HD-SDI. We first noticed it when we switched our feed from HDMI being looped through a TVlogic back to the SDI output. It definitely looked cooler and brighter than what we had been seeing. We ended up going back to the HDMI(so the DP could see the exposure tools at village, that only worked with the HDMI until the recent firmware fix). I confirmed the difference comparing SMPTE bars coming out of each output.
This may be useful information the next time you trust lighting from either of the signals coming out of the camera. I guess you trust your light meter, maybe the RED lcd and your RAW exposure tools. Even with calibrating a monitor to the bars coming out of camera and you light to the image, you may not be lighting to an accurate representation of the image.
A test should be done with an Epic. I'm interested to know if it's the same.
I attached photos of the color bars. The first one is HDMI the second is HD-SDI.