1) It's been covered in many forum posts, but yes it works native with GE=No and OpenCL works correctly
2) This question is perhaps over simplified. Will it matter? depends entirely on what you are doing. VRAM doesn't add any speed in the absolute sense. VRAM is specifically useful if you are working on larger resolution projects, or in other cases where larger amounts of data need to be processed from RAM. For instance with 4K projects it makes a huge difference. If you're in 1080p land and going to stay there for a good long while then it won't matter as much. It also depends on how many and of how high resolution your monitors connected to the 770 are, since the VRAM is shared between framebuffer needs of outputting the image on the monitor as well as to load data into for processing via CUDA and OCL. So you need to make that decision based on the type of work you are doing.
3)In what sense? if its Rev B it won't work any better than it does in a hack. the OCL bug has to do with the rev and the drivers, it has nothing to do with hackintoshes. Otherwise, it seems all 7XX cards should work in a mac pro albeit you will not get any display output until the OS has loaded. You won't see the apple boot logo or be able to access drive selection via ALT key, etc. If you have the slots you can always add the 780 as a second card and use it for processing without any monitor attached.
g\
