nice. helpful. I think what the OP is looking for is a list of difficulty level-specific modifiers.
http://forums.civfanatics.com/showthread.php?t=387484 post # 7
also you can check it out in the CIV5HandicapInfos.XML file.
what gets me is that they have plenty of challenges that aren't difficulty level related, but they don't really increase the difficulty level for the human player at higher levels they just make it easier for the ai. give the human a 5% happiness penalty on king, then ramp it up to 20% by diety. -5% combat penalty that ramps up by difficulty, things like that. and especially don't start deity out with the same amount of happiness as emperor. how about a barbarian PENALTY of 10% on king that ramps up to 40% on deity? and for god's sake give the ai a research bonus!
/rant