float[] → Vertex[] – decreases performance by 1000%

[David]

> Hm. Do you ever do pointer arithmetic on Vertex*?  Is the size and
> offsets are correct (like in Vertex vs float)?

No, yes. I really have no idea why this happens, I saved the contents of 
my buffers and compared them with the buffers of the `float[]` version 
(thanks to `git checkout`) and they were exactly 100% the same.
It's a mystery.