Hey late at night I found the problem! It's nothing related to drawing the quads, it's about the text!!! :x

I was rendering text using DX methods. Both the creation of the font interface, and the drawing of the font are incredibly slow. I measured around 0.0013 milliseconds for each, which is several orders of magnitude the time required to draw a 3D cylinder. Even drawing an empty string takes all that time.

I'm not using DX fonts any more!!! :evil: