Please don't reply to terrible posts, just report them. There is a wealth of information they could read in this thread on the topic. Also a reply of "I read something (but I can't point you to it) and my feelings are..." isn't useful either. Thanks.
I remember a reply (I think it was in the thread here) were someone compared the haste vs. mastery cases on a boss fight and obtained nearly the same dps. Although it was only one example, my feeling from playing around with FD and Simcraft, from the discussion here and also taking into account my practical experience is, that the difference between haste and mastery is very small dps-wise. So maybe it really comes down to the personal preference and how it fits your playstyle and maybe also the boss mechanics.