Small changes to the best quality default speed trade off.
Some speedup settings are worth while even for best quality as they
have only a very small impact on quality but a significant impact on
encode time.

These changes give as much as a further 50-60% increase in encode
speed for my test animations clip with minimal impact on quality.

For this sequence these changes improve the best quality encode  speed
to about the same level as good quality speed 0 in Q3 2015 whilst
retaining the large quality gain of over 1 db

For many natural videos though the quality difference from good 0
to best is much smaller.

Change-Id: I28b3840009d77e129817a78a7c41e29cb03e1132