The topic pretty much says it all. I'm studying with a fairly good over all 2kyuu study book, but the only problem is that it lumps nishiteha warini, and kuseni all together and explains them very poorly. Actually, it doesn't explain them at all. I've checked jgram.org but I haven't found much more of an explanation of how they are different.
I don't suppose anyone knows how these suckers are different? Kuseni isn't too bad, it is more of an accusing tone, but the others...
Are you talking about a comparison, for example, between X にしては and Xの割には "for an X" that can be paraphrased as "considering the fact that it is an X。。。" there results a state/condition that different than the one normally expected ?
Simple sentences without a clear distinction in meaning the two:
彼は、子供にしてはとても背が高い。
彼は、子供の割にはとても背が高い。
これは日本のレストランのわりに、値段がやや高いですね。
これは日本のレストランにしては、値段がやや高いですね。
A rambling list of situations in which one or the other is commonly used:
1.年・年齢にしては、若く見える I would say 年(年齢。。。)の割には、若く見える
In case of doubt, reframe as 実際の年よりは.

歳にとしては is comparatively acceptable, if not natural, idiomatic Japanese ?
2. Cases in which a self-comparison is clearly implied will never take (君、彼。。。)の割りには、
Ex.: 君の割には、それがいいね。should be 君にしては、それがいいね。
3. にしては restricted to the use following nouns only
割りに links to the noun with の but can also come after verbs, adverbs or adjectives.
4.8月のわりには寒い。(Less encountered)
8月にとしては寒い。(Suggested

)