The answer is always, "it depends". Luke Humphrey discusses it here:
For me personally it has been the following:
First Hansons from 3 days per week - 16% (4:20 to 3:38) - Nov 2014 to Oct 2015
7 months more Hansons - 4.7% (3:38 to 3:28) - Oct 2015 to May 2016
5 months more Hansons - 2.3% (3:28 to 3:23) - May 2016 to Oct 2016
3 months more Hansons - 1.4% (3:23 to 3:20) - Oct 2016 to Jan 2017
Daniels + 3 months Hansons - 3.4% (3:20 to 3:14) - Jan 2017 to Oct 2017
Under the right circumstances that last jump would have been more like 8.4% if I had gotten around a 3:04.