In the original beta build the amount of mana returned by vampiric touch was reduced from 5% to 2%. I know enough to be confident when I say that's a 60% reduction in the amount of mana returned.
MMO Champion is today carrying a quote from Blizzard on this very spell, in which he implies the actual value is 2.5%. The talent calculators still read 2%, but if this is true it would represent a mere 50% nerf to the current spell. Let's work with that optimistic number shall we?
I can't check the whole thing because I'm at work and there are firewalls and other draconian obstacles to my research, so if I've taken this out of context I trust you to put me straight, but what the quote says is:
To be honest, 2.5% still might be too high. In our tests, Shadow Priests were still providing around the same amount of mana to their party (if not more) than before because of their increased damage output. Not to mention the Priest wasn't going out of mana at all because of Spirit/Improved Spirit Tap.
This is where I do a bit of cyber head scratching. Same amount... if not more?
If I spend ten minutes scribbling notes on a bit of paper, then give up and go ask a numerically literate friend for help, I can work out that to return the same amount of mana through VT with a 50% nerf to the mana returned in place, you would need to sustain double the damage. That's 100% more, apparently.
So what this guy or gal is saying is that in their tests, shadow priests were pumping out TWICE the dps.
I want to know more. A lot more. Like what kind of tests? Were the shadow priests at the same level in idential gear with the same spell damage fighting the same mob with the same buffs and debuffs?
They'd better be if you're gonna make statements like that. The same amount!
I find it very hard to believe that simply with the changes to priest talents we have seen so far a like-for-like priest would pump out double damage.
Admittedly, maths is not my strong point, but I'm beginning to wonder if it's Blizzard's either. Place your bets now for math failure of the year...