RE: RULE hint better sometimes after 10.2.0.3 upgrade

I'm not aware of any specific CBO issues between 10.1 and 10.2, but you might want to have a look at this list of common issues for 8i-to-10g upgrades since possibly some of the changes mentioned didn't occur until 10.2: http://www.freelists.org/archives/oracle-l/07-2006/msg00516.html  

Beyond that, I'd recommend to BAAG
(http://www.battleagainstanyguess.com/baag/) and I think the best way to do that is look at 10046, and possibly 10053, traces of your problem queries running on 10.1.0.5 and 10.2.0.3 and identify the key differences.  

Regards,
Brandon

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