I tried a short test of the experience modifier. My mages are level 24, so no quest bonus'. Mob kills were the same, but the amount to level was changed from 31,700 to 27,200 to go from 24 to 25...roughly 14%.

Very gross test but just wanted to get an idea. I'm not going to spend time testing them up to 30, so I x-ferred my lvl 38 toons over. I'll wait to see what they have to say for the quest exp modifier.

Edit/Update: Level 39 to 40 changed from 85,700 to 70,200 exp points (roughly 18% less).
Ran SM 1 time. Didn't see any loot changes, but I heard from posts on the WOW forums that Doan has a chance to drop an Epic ring. Will have to check it out.