I think the 600 will give you around the same flow as a dual unit, hard to say which will be more, there too close to call.
The advantage in the dual unit, comes in having two seperate flow circuits.
Your not trying to push 160GPH through a GPU coolant block first.
Disadvantage is more pumping
As most of you know, thermo eff curves flatten out around 4-5 L/m on most blocks, hence I see no reason personally, to push 160 gph, however you may find different.
There seems to be mis-understanding about flow, at least what I have seen.
Once a blocks thermo curves flatten out, thats it, pushing 2X or 3x the amount of water at it will not help.
If this wasn't so, cars would have small rad's and big pumps, since rad's are more expensive, and hard to place
I can tell you how we test cars, which believe it or not, applys to computers.
We determine the thermo eff of the engine block, based on cooling flow, and once we see the curves flatten,we have the ideal flow required. Then we design the rad and placement.
Of course there are limits, if we have to make the pump or rad too big, the engine designers have to go back an fix there issues.
BTW Don't worry about the price, had no idea market was this big. Spent all last night making new extrusion dies, so we can make these pumps quickier, and likely cheaper. New case is 3-5 weeks away, will still be color anodized AL and hopefully people will find it just as attractive.