Air is gonna do fine. The bottleneck in CPU cooling right now is pretty much always the transfer between the die, the heat spreader and the cooling plate, not the transfer from the fins to the air. Water cooling can do slightly better because you can keep the water cool, and with that the cooling plate, and through that increase the heat flow from the CPU to the plate, but it's really only marginally better than a big air cooler.
And if you put more dies below a heat spreader, you get more surface area, i.e. better heat flow overall (compared to a single die with the same power consumption) from the dies to the heat spreader and from the heat spreader to the cooling plate.
That's also the reason why bigger air coolers don't really do as much as you'd think they should in terms of cooling performance or overclocking, the difference between an NH-U14S and an NH-D15 is really quite small. If the problem is heat dissipation through the fins all you have to do is make the cooler bigger.
You can bring water closer to the crystal, and make it pass faster past / inside the dissipator plate, thus achieving a larger stream of heat. Effectively you can turn the dissipation plate into moving liquid with high specific thermal capacity (5-7x of the metal plate).
And if you put more dies below a heat spreader, you get more surface area, i.e. better heat flow overall (compared to a single die with the same power consumption) from the dies to the heat spreader and from the heat spreader to the cooling plate.
That's also the reason why bigger air coolers don't really do as much as you'd think they should in terms of cooling performance or overclocking, the difference between an NH-U14S and an NH-D15 is really quite small. If the problem is heat dissipation through the fins all you have to do is make the cooler bigger.