Answer
There are many factors that influence the ability of a video card to process a TIN in ArcScene. The video card, the video card driver, the amount of RAM on the video card, the total amount of data being rendered in the scene, and many others. However, as an approximation, the numbers of nodes in a TIN that a video card can process are as follows:
128 MB on a video card = approximately 300,000 nodes
64 MB on a video card = approximately 200,000 nodes
32 MB on a video card = approximately 100,000 nodes