All depends on what kind of rendering you are talking about...

If you are using a GPU powered render engine and you want to spend under 700-750USD you have only ONE valid choice : NVIDIA GTX 1080 Ti!
Or if you can spend more you can build a powerful rig with a pair of 1080 Ti.
But in that case you have to build a very powerful rig with a very efficient cooling system and a powerful CPU/Mother Board.

But if you really NEED the Quadro line and want to get (almost) the same speed of a single 1080 Ti (and even better) you are forced to buy a super expensive Quadro P6000 that costs about 6K USD!!!!


I have an overclocked version of a "Gtx 1080 Ti" and I usually use Thea Render with the "Presto" engine that leverages on the GPU and it's very very powerful and fast.