I know you like to get excited about faster and faster GPUs, but keep in mind what you're using it for.
As far as Resolume is concerned, at this level the extended 3d capabilities of a Quadro are not really doing much for you. When you want to draw millions of polygons in AutoCad, a Quadro is great. Most of the time, Resolume just needs to draw a few quads and texture some pixels on them. Even the 3d OpenGL effects are highly optimized, so with normal use, they're not scraping the bottom of the barrel.
When you are talking about these kind of cards, your bottleneck is most likely to be the connection from your motherboard to the GPU.
The pixels of your videos are stored on a disk. They need to be uploaded to your GPU, where they will then be used as textures for the quads that are your layers and slices. These modern GPUs can all process them fast enough, and a SSD can read them fast enough.
At this point, you're probably more limited by how many pixels you can push through your PCIe x16 slot, rather than the processing power of your GPU.
If you want to get a good GPU for Resolume, just pick the card that has the most practicality. 4 outputs sounds pretty sweet. I would go with that over anything else.