Quick update for tonight. I've written a controller that can handle multiple vertex buffers. I wanted to stress test it, so I ran it until I ran out of memory. I have a pretty shitty video card, but I topped out at ~3 million cubes, a little over 3 million vertices and 531 chunks (each chunk is 16x16x128). The first screenshot is from the first stress test while the 2nd one is the test where I ran out of memory.
The other awesome part is I was still averaging 63fps :]