I absolutely think it's worth water cooling GPUs. Over the past 10 years or so that I've had custom water cooling loops, I've found the main benefit to be in noise reduction, not so much performance. I hate anything above almost a whisper. You can get a lot of cooling potential if you're willing to go with a big case and good amount of radiator capacity (lots of fans at lower speed) and maintain noise levels below the ticking of a wall clock. Even well cooled AIB GPUs tend to get pretty noisy when you're running them at 100%. On the other hand, due to the way GPU manufacturers lock voltage and find other ways to limit performance through overclocking, I've never found that water cooling buys more than maybe 5-10% performance above an air OC with a good fan setup.