I would like to see parses rather than I did X amount of damage on a target dummy.
For example,
http://raidbots.com/epeenbot/us/zul%27jin/vyroxx/ does not do that, and his parses are consistently top 5% of priest or even #1.
If you look at his ultraxion he is mind blasting on CD the entire fight, where as only 17.3% of the fight if he has 100% dot uptime he should be using the mind spike rotation. Look at the amount of damage from mind spike vs mind blast and the number of cast.
You also have to take into account you could lose shadow fiend attack orbs waiting for MB to get orbs. The only benefit I could see to casting mf for a tick would be to get arch angel stacks for when you go to redot, and even then you are still probably going to have to channel a full flay.
Like I said, provide me parses and I'll believe it.