Hey BLackburst,
I understand your frustration, its seems absolutely nuts that Nvidia can’t guarentee tear-free, frame-drop-free, performance from their Geforce cards in a simple scenario as you’ve outlined. However, as some other posters have pointed out, the Geforce cards can get you very far, have excellent power, and in some situations with certain displays and settings can produce completely perfect results. However, the caveat… it is not guaranteed on Geforce hardware, straight from Nvidia’s mouth. This is a hardware and hardware driver matter, and here at Derivative we do not want to misinform our users about what the Geforce cards are capable of.
Its get much more complicated and the results are more varied when you are talking about multiple displays and multiple GPUs. Nvidia’s answer for the customer who needs complete frame perfect performance is to move to their “professional line” of Quadro cards. This is why features such as SLI Mosaic for multiple output spanning and G-Sync for multiple GPU framesync are also only available on the Quadro line. They are not shy about this fact either, check out this Geforce link and at the bottom they clearly have a “Professionals” paragraph that links directly to their Quadro features.
Our recommendation is that you decide what your requirements are based on the project. In many venues, certain budgets, certain clients, a frame drop is tolerable (90% of people probably never notice frame drops, while 90% of the people on this forum will scream when they see it 
). In the case where frame drops are a show stopper, you are hopefully dealing with a client that is budgeting for those extremely high production values, and thus budgeting for Quadros is the price of admission to guarantee that level of performance.
We often recommend Quadros since many of our users are going big with multi-display, multi-GPU solutions, and in those cases the overpriced Quadros come through. We’ve spent many years working on Nvidia GPUs to get perfect playback, and the complexity does go through the roof when you are trying to eliminate that last frame drop in your 1 hour long show. We are also aware it can be hard to find all the relevant information in a quick, digestible format; we’ll continue working on improving that information to make it easier to find and understand. When you are having trouble finding something in the wiki, please just post here and we’ll try to point you in the right direction and make that topic easier to find for the next person.
To answer your AMD question;
AMD we only recently started to officially support. For years their openGL driver implementation was behind, but it is getting much better now so we’ve spent the time to get AMD up and running. Since this is a newer development, we actually do not have much field time with AMD cards, and their different product lines, so we don’t have much to report in the way of benchmarks and/or tearing and frame dropping. Also, there are a couple of features in TouchDesigner that are still Nvidia only such as CUDA, H.264 realtime encoding, and the Blob Track TOP. We still recommend Nvidia first due to these facts.
If you are just starting with TouchDesigner, I’d recommend getting a Geforce card first. They have great performance per dollar, and you can go top-of-the-line Geforce for a fraction of the price of a Quadro. Once you start learning the ins and outs of TouchDesigner, Quadros will be there if you need them and you won’t have spent any unnecessary money if you don’t.
Cheers