Early-Z, FBO, HDR

I played with Early-Z today, and I must say I’m impressed so far, simple to implement and gives nice speedup if used correctly, but…

Early-Z seems to be OK as far as work is with simple rendering, objects+shaders. I on the other hand have situation where I must render scene to fp16 texture via fbo, then use this texture to do HDR and get final image.

From my experiments I found that Early-Z seems to give no speedup in heavily redrawn scenes under such conditions.

Is this FBO, FP16, driver, hardware or broken code limitation???

6800GT FW-76.41