Pixar doesn't use GPUs (much). Their render farm compute is mostly CPUs with a ton of cores + memory, using AVX-512 and SSE 4.2 optimizations when appropriate to optimize render time. Why? GPU render compute doesn't speed things up as much as you might expect. Yes, in certain instances, you can get a 3-4x benefit, however you have to fit all the polys in GPU memory. Paging back out to system RAM brings you back down to CPU speeds. Scenes can often contain > 150,000,000 polys. Only very recently have gpu memory sizes gotten big enough to be "worth it" over CPU rendering, and even then, it's often less flexible/tolerant of mixing older architectures in the cluster.