/pwn'd by gilga!
Gilga is the guilds leet druid, so listen to him! I suggested the whitemend because the mana regen is REALLY close, and you have a bunch more +healing.
Warning Math Content: (And since i did it, it's most likely wrong...)
In 2.4 Blizz changed the way mana regen works. Intelect now plays a roll in your regen. It's also important to remember that mp5 is regening all the time at it's advertised amount. Spirit/int only regen at 1/5th it's full amount while you are casting.
So here is what i came up with in my head...
The leather items would give him the following stat bonus...
all armor-
int-375
spirit-374
just 2 leather pieces-
mp5-0
healing-145
The Whitemend set with 4 royal nightseyes, and 2 luminous noble topaz would give the following stat bonus...
all armor-
int-361
spirit-308
just whitemend set-
mp5-30
healing-195
So based on baldeys stats (358 int, 332 spirit), a 7 min fight, where he uses 1 innervate...
With his current gear he would regen 153 mp5
Whitemend would give him 173 mp5
The leather gear would give him 177mp5
If the fight went to 12 mins, but he was unable to use a second innervate The number would be...
With his current gear he would regen 131 mp5
Whitemend would give him 148mp5
The leather gear would give him 145mp5
So the bottom line is depending on the length of the fight, based on regen, in short fights the leather could be better, in longer fights, the whitemend will be better. But regardless, the whitemend has and extra 50 +healing.
Now we need miri to figure out how to compare 50 +healing to between + or - 3-4 mp5... my brain hurts. gilga, can you make a venn diagram?
oh, by the way, i didn't do this in my head, i used this...
http://www.resto4life.com/guides/calculator-mana-regeneration/