The red sensor is 60% VLT and the sensor is 70% VLT. I have both, along with platinum mirror and ignitor mirror. I used to think the red sensor was the best for flat/cloudy/overcast days, but in flat light the regular sensor is hands down the better lens for me.
I'm still trying to figure out how to use the others. The ignitor mirror seems to be a great all around lens, even on blue bird days and does amazingly well in all but the worst conditions (flat light/fog). I like the Platinum but with the great lower light ability of the ignitor it makes a perfect lens for blue bird days and the changing sun patterns that leave shadows all over the slopes.
To keep it simple the sensor/ignitor mirror would be all that's really needed. Make a bit more customized and it's red sensor for overcast/light snow, platinum mirror for blue bird, sensor mirror for flat light/stormy days and ignitor can be forgotten about.