I did a production this week with 2 50′ foot cables and a 100′ cable and they carried signal with the help of $20 HDMI In-Line Extenders (Auvio-the company who made them) I purchased from Radio Shack. The set-up was the longer cable from the camera to the In-line Extender and a 3′ Cable to the ATEM. It worked wonderfully. I should note, that the 100′ cable I purchsed has an additional signal booster built into the cable as well so that might have helped the 100′ signal, but the 50’s were stand alone cables.
100′ Cable from KanexPro with built in Signal Booster
2 50′ Cables from Xtreme with Ethernet 1.4
3 Auvio HDMI In-Line Extenders
I hope this helps! It worked great for me.