Two corrections: the viewfinder doesn't have 5.76 million pixels but "dots" ie subpixels. It has 1.9 million pixels, 1920x1080 resolution.
The removal of the colour filter array doesn't and physically cannot make the sensor much more sensitive to light. The difference is only 1/2 to 2/3 EV, depending on how much infrared light (which will blur the image) they filter. This is less than one stop..
Missing my Pentax 6x7 now..