And the answer is...?

Yes, yes, and yes!
It does all fit...
I have room for a picture of my lovely wife...
AND I have still room for a full roll of toilet paper!

I must say, it was getting close, but below the prove that I was successful!

 
Getting everything inside all 4 panniers was reasonable easy. The difficult part is to do this while:

1. The weight is evenly distributed on left and right.
2. The rear panniers maintain heavier (kinda easy since they are bigger)
3. Items are organised in order of "accessibility"; gels, wind jacket on top - tools and new clothes at the bottom.

During the packing I used a scale to check the weight and move things around. The rear panniers weigh 13.8 and 15.2 lbs, while the front panniers ended up weighing 8.6 and 7.8 lbs. That is a total of 45.4 lbs.
Now add the weight of a full "tank of gas"  (three 20 oz. bike bottles with water) and we hit the 50 lbs. How is that for a workout?!