64GB RAM in a Quad-Core Nehalem?

Just got given a Mid-2012 Quad-Core Nehalem (3.2gHz) Mac Pro (4 RAM slots).

I would like to max the RAM out in it using 4 x 16GB RAM modules, and have hit an information snag as far as exactly whether or not the Quad-Core machines specifically can see and utilize 64GB RAM in a 4 x 16GB module config.

I know the original Apple "Party Line" about how much was 'officially supported': 32GB (4 x 8GB). I also know that some sources have said that the Mid-2012s can use either 48GB or 64GB.

Now, there are some sites that say that ONLY the 8-core machines are capable of using more than 32GB, as they had 8 RAM slots. There are others that seem to imply that ANY of the Mid-2012 models can use 64GB, as the 32GB limitation was only due to the version of the OS that shipped with the machine ("Lion"), and once you update the OS to Yosemite or above, that 32GB limitation goes away, and the Quad-Core machines can utilize the 4 x 16GB config.

I plan on starting out running Yosemite on this machine, and possibly going to El Cap eventually. I would really like to put 64GB in this puppy if at all possible, but need clarification on whether or not it is actually possible.

Does anyone have the definitive answer to this question (before I go and blow the cash on 4 x 16GB RAM modules)?

Thanks in advance.