I had purchased a 75ft hdmi cable from ebay just to test and see if it would even work without any noticeable video loss and it had a built in amplifier in the end of the hdmi cable and we tested it back and forth with a shorter hdmi cable and could not find any noticeable loss.
Surprisingly it really did not have any noticeable loss but I also think it depends on what is on both ends. We were using a high end graphics card that has a hdmi out built into the card and we saw no difference in picture but did not test it with any kind of DVR's.
We do only install QVIS dvr's so I am curious if the graphics card on the dvr's can work with a longer hdmi cable (75ft)