Which A/B test gives the best results in email marketing?

Recently, Mailchimp published in its blog a study about the tests carried out during 2013. From this article, the table with the data on the type of test carried out and the results obtained has caught our attention:

As was to be expected ehe issue test is the most commonly used test, followed by the time of sending test and the sender's name. What is striking is that the huge quantitative difference between the subject test and the time of sending and sender test is not justified by the results obtained. In other words, the test in the case is the one showing the lowest rate of improvement. in both openness and click-through (although we must also ask how representative each sample is, and whether the lower figure is due to a higher number of tests analysed).
In any case, it is also worth highlighting the figures that show tests at the time of sending, with more than 20% improvement in click-through rate.. Some of the tests we have carried out at Digital Response corroborate this idea, as some of the biggest improvements we have seen have more to do with click-through rate and timing than with open rate and subject line (despite what is often thought).
The greatest influence on the opening of emails, also contradicting the more general thesis that bets on the subject line, is produced by the variation in the senderaccording to this analysis.
Does your experience match the data provided by Mailchimp?