I just use Lenient as it does enough to get the black levels up below sync which I have had cause problems. It also does a RGB to YUV conversion, cannot say I'm 100% familiar with that area.

Tecnichaly the minimum level should be 16:16:16 for blacks and maximum 235:235:235 for white. If its only for viewing on TVs rather than transmission then going over 100% white doesn't seem to cause any grief and a lot of stations just don't seem to care much, if you are worried about it though you can use Conservative or Extremely Conservative.

I'd suggest best thing is to look at what your levels are using the histogram scope.

Easiest way is to apply the filter to the video bus.