You would have the same framing with the 50mm at 10' as you would with the 85mm at 17'. As Neuro pointed out the relationship of distances will change because you are farther away. In some ways depending on what you are trying to do the 85mm might be better than the 50mm for groups, or the 50mm may be better. For instance if you were taking an outside group photo you might prefer the 85mm because of compression of a distant mountain range or building would be more pronounced in your picture. Or you might prefer the 50mm indoors because of framing.
I would prefer the 85mm f/1.2 myself. I think it is a better lens overall. At 17' the full frame the 50mm would have a 12' wide framing and the 85mm would have 7'. Still not wide enough in my opinion for a good indoor group picture lens.
I suggest you consult a FOV calculator and enter the parameters of how you usually shoot and determine what would be the appropriate length.
http://www.tawbaware.com/maxlyons/calc.htm
As for those two lenses, the reports you have read are correct. But they are both L lenses and at their respective length they are the best. So to me it is a length question that decides which one.
Edit; missed that you were using the full frame and revised.