Fresh takes a second place black. Gray just has to be resonable to me.
1) I can carry more fresh in a bladder on the roof, not fun, but doable and I can get 5 gallon jugs also.
When black is full, you have to dump and there is nothing you can do about it.
Grey, I can usually let some out if it's full.
In a TC, 50+ fresh is good; under 35 black and I won't look at it, 35 gray is ok, but acceptable.
To me, the 55 fresh to 59 is fine, because it's more important to me than gray. I try to dry camp in the middle of nowhere as often as possible, so any reduction in fresh is bad. Black increase would have been a better trade to me.
All in all, fair trade. Not sure about the ratio though, 55 to 59 buys 4 gallons of fresh, but you loose 9 gallons of gray.