I do use a P40 for my machine learning box, but I'm curious how you put three on the same system, given they need a CPU power plug and a pci-e port. Then, to cool them, you need to plug your own cooling system, requiring more specific power plugs to be available. What kind of chassis, motherboard, power unit you use to do that? It'll certainly will cost more than $1000 anyway, especially since you also need a decent amount of RAM to preload the models before you move them to the GPUs.