Is there any performance difference between unique and no unique index

Hi,
We are working with both databases Oracle and MS-SQL and we have an open channel to MS-SQL server core team.
We got the word from them that there is a difference between unique and no unique index from the optimizer perspective, i.e. the optimizer knowing that the index is unique may choose a more suitable plan for running a specific query, we're still trying to find a specific example.
Anyway, since we do not have an open channel to Oracle core, I thought maybe one of you guys knows something about Oracle optimizer behavior on this issue.
I am interested verified answers from certified sources and not suggestions or thoughts.
Thanks in advanced,
Tal ([email protected]).

Maybe, you will like to check this link for a similar question answered by Tom Kyte
http://asktom.oracle.com/pls/ask/f?p=4950:8:385900000490041683::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:7641143144618,

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Is there any performance difference between unique and no unique index

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