Interestingly, if I set async_depth to 64 instead of default 2 speed of encoding full HD 29.97 fps h264 file increases from ** rendered 9133 frames in 442.712 secs, 20.630 fps to ** rendered 9133 frames in 337.237 secs, 27.082 fps so may be try this setting and see if results in higher fps for you?