There’s a marginal difference in watercooling and good aircooling. In regular usecases a good towercooler and a water cooling system reach almost comparable temperatures, the watercooling begins to show it’s perks once you start to overclock, bump the vCore and reach critical temperatures.
In this case the watercooling will hold the temperature and the aircooling will has its limits and can’t cool anymore.
What is also important is that you have a good airflow inside your case. Every cooling system can only cool down a delta Temperature.
If you got 22°C room temperature, and 50°C air temperature in your case because you’re not venting it right, and your cooling system has a deltaT of 20°C you’ll never get below 30°C because of the temperature of the air in your case.
If you vent it good and got 25°C in your case, you can always reach room temperature.
And the average graphics card running with 70-100°C boils the inside of your case. It’s more important to get the air out of the case than having a super efficient cooling on the graphics card.
That said, watercooling bypasses this issue. Usually your radiator is mounted outside or on the top and directly cooled with air from the room. The energy (heat) is transported by the water directly from the cooling block to the radiator and the heat expelled there to the room-air, bypassing the hotter air in the case.
However, specially for CPU watercooling you need additional cooling for north/southbridge and the voltage transformers around the CPU. Those parts are usually cooled with the airflow of the CPU cooler.
Not to mention that a good water cooling system for CPU+GPU costs around 400-700 bucks and has some maintanance effort to put into.
@price difference of graphic cards:
There are chip manufacturers, AMD, Nvidia, which produce GPUs. They usually produce reference cards, which are directly from AMD/Nvidia. And then there are the board partners. They buy the GPUs from the chip manufacturers and create their own board designs, memory amount and cooling solutions.
The major differences are the type of cooling and the quality of the parts.
It’s no secret that “all” of them produce in China, as cheap as possible, still there are differences in the quality of PCB and especially the capacitators on the cards. Remember the disaster of many ATI and Nvidia cards, twirping due to low quality coils under load, to graphical artifacts on the screen because cheap capacitators failed, or simply a black screen because one of the liquid filled capacitators blew out?
Today most use solid capacitators but there are still quality differences between them.
It usually reflects directly in the price.
So as a rule of thumb, the more the card costs the better the quality…
However we reached a point where GCs are changed every 2-3 years and quality is a lot higher. Who cares then if the card lasts 10 or 30 years?
Which leaves the most important issue… the cooling system.
The reference cooling usually is complete crap. Bad temperatures and loud like leafblowers.
You either buy a cheap card and buy an aftermarket cooler from Gelid, EKL, Scythe, Thermalright… however you need the balls to disassemble your newly bought card, and you void your warranty. Also you can add another 50-100 bucks to the pricetag for the cooler.
Or you buy a card from a boardpartner with a good cooling solution, such as ASUS’ DirectCU, or MSI’s TwinFrozr.
Effective and smart cooling with low noise even under full load.
You should also keep an eye on the warranty times they offer, and read up on the internet on problems with their support and warranty to pick a board partner.
And lastly it’s the gimmicks and gear inside the box. A retail card just in an anti-static bag is usually cheaper than a boxed card, with adapters and cables and maybe 3 games included and a poster and whatnot.