I wanted to expand on this, to try to clear this up. It seems that a scroll plane was used for the ocean in Panzer Dragoon Saga, which should have had a limit of 8192×8192 pixels. With the 3D infinite plane able to reach 4,096 pixels, I'm assuming the 3D assets-like pillars in the ocean-fall into this category. Of course there is also a limit of how many polygons can be shown per second in a scene. Does that seem right?
EDIT: I was also looking at the draw distance of Tomb Raider and Sonic R. The latter has all kinds of uneven and spiraling geometry. I find the graphical cutoff easier to quantify in Tomb Raider, because it features a human in a somewhat realistically-sized environment. For instance, we could assume Lara Croft is around 5' 6" tall, so the sizing might be easier to visualize.