There would be no performance difference. But it will help you to keep your memory at lower temperature, thus increasing overclocking potential.
It all depends on your motherboard. If there is space for bigger heat spreaders, then go for it. On some motherboards you cant really install such modules because it will prevent either your cpu cooler or your videocard from fitting properly.
There can't be "overkill" when you are talking about such small amount of memory as 32GB.
Its true, that no modern game would ever use more than 10GB, and that OS+background applications would not use more than additional 4GB.
But it will allow you to gain performance increase.
The most obvious way would be to create a 16GB ramdisk.
Than you can move your swap file to this disk and gain a significant performance increase. You'll see how smooth alt-tabing can be if you have swap on ram disk.
Its not a secret that windows writes data to swap file all the time, no matter how much memory you have. Disabling swap file would not help, because instead of caching applications will just drop unneeded data and then get it again from their files. Some applications can act weird without swap file. Ramdisk swap file can do miracles.
Or you can just install your favourite game to this RAM disk and get almost instant loading. (hint: you need much more memory than 32GB to install wow on ram disk
, but for most games it works just fine)