i wouldnt trade dmg for haste until they finish their system.
currently we dont know what the haste cap will be, or how big of an effect it will have.
QFT
In regards to the damage vs. distance bit I have visions of a tank shifting position causing the mob to move and the monks REAMING him for it. "Could you hold the friggin mobs still?! We were in PERFECT position!!"
Like some crazy artists telling their subject "Don't move an inch! Just hold that position..."
You're right though, it could very well be worth it, especially on long fights where the mob doesn't shift much (doesn't knock around the tank, stays in one place and just summons, etc. etc.). Of course, using shadowstep we'd (in theory) be at pretty much the right spot too so we'd prolly end up using that a ton more.

I just love it when the server tells me "you have no line of sight" and I'm like "but...but....the mobs right there! He's right in front of me!"
*shift around and adjust position some more*
"you have no line of sight"
/cry