over kill lol.
anyway, the smaller the water volume, the more helpful UV is. Bigger water volume means more water have to pass through UV to kill parasite. in very huge tanks, people more often than not run more than 1 unit simultaneously. Think of it this way. (scenario exaggerated to prove a point). it's more useful to run 10 units of 36W UV than a single unit of 100W UV. the amount of water passing through so many (10), units of UV is much better than passing through one 100W UV. increasing the wattage isn't going to kill the parasites any faster. parasites die in 36W, 55W and 100W all the same speed. just like if i shoot you in the head with a shotgun, machinegun or a bazooka. you don't die faster from each of those. you die at the same speed right?
also depends on what fish you keep. in a tank full of hardy fish like fairy wrasse, damsels, anthias and/or other bullet proof fish, the reliability of the UV system is questionable since these fishes are so disease resistant, that the effect of UV is almost, if not, same, to a system without UV.
Testing UV out in a tank with very disease prone fish like tangs, angels and butterflies will see more results on wether or not the UV is working or not.
Also if your tank is already on the verge of crashing due to disease outbreak, installing a UV there and then probably won't be of much use. UV is good for preventing disease from reaching catastrophic levels, but is useless if the disease has already progressed to that stage.
As for wether i am a believer in UV, yes i am. a firm believer at that. But UV is not as magical as everyone makes it out to be, and will not catch you every single time you fall. Just because you have a UV, does not mean you can be very liberal and throw in 5 tangs, 5 angels, 6 butterflies at one go and think that you will get away with disease outbreak.
Slowly stocking your fish is important so as not to increase parasite load so quickly that UV cannot cope. you need to work with the UV, not against it