I did a rendering test (audio only).
With the old flac:

9063 frames; render in 2.08s; 4340 fps.

With the new flac-1.4.0:

9063 frames; render in 4.471s; 2027 fps.

Basically, the rendering speed has halved. In my opinion, it is not
worth upgrading (it was better to keep the "useless" optimizations in
assembly!).

I agree with Andrea.  The very small test I did for audio only had the same deplorable results:

OLD:  ** rendered 2712 frames in 0.190 secs, 14273.684 fps

NEW:  ** rendered 2712 frames in 4.646 secs,     583.728 fps