过度 and 过分 are both adjectives meaning "excessive, undue, over-", but how can we distinguish between the two when writing or speaking Chinese?
I'm not 100% sure on this one myself， it's appears that they are interchangeable for emotions such as 过分高兴 and 过度高兴. I asked a Chinese friend about the difference between the two; she replied "个人认为没啥区别，但“度”比“分”成分多" - not really helping that much.
I have broken 过度 down to two common uses:
1) describing something that you do to yourself like 饮酒 or 减肥， or even 过度治疗
2) describing an emotion 过度兴奋
过分, according to my dictionary, is used for “说话，做事”; i.e. doing something or speaking excessively. I think it emphasizes reacting excessively or "going over the top" perhaps. Rather than an objective quantity emphasized by 过度1， 过分 implies a subjective consideration of the preceding action. i.e. you are making a judgement on what has happened. 过度 appears to be more neutral/objective in this regard.
Consider this example: 因为老公过度喝酒的问题离婚是不是太过分？
This fits in with my above explanation; we have the seemingly quantifiable “过度喝酒” with the subjective reaction from the writer.
Does the common collocations 过分要求，过分强调 fit this explanation as well? I would suggest that when somebody makes a 过分要求， they are reacting based on an understanding of what is being explicitly or implicitly offered.
For example, when a customer walks into a shop, there is an implicit promise that the staff will offer the best services possible. When you 过分要求 a staff member, you are overreacting (反应过度) to the understanding of this tacit agreement.
What do you think?