index + table monitoring performance

Friends,

We have the utter most critical database in the bank which is used for share trading appliction. The database runs on AIX 5.2L OS with 12 cpu and 24GB of RAM. SGA is around 3GB and PGA is 2.4 GB. We are planning to enable index monitoring on application schema, this schema is heavily accessed during trading hours, i.e. 3 hrs. in the morning and 3 hrs. in the evening, though its 24x7 database, and number of transaction per second are 120. Could you please shed some lime light or suggest us as per your experience that enabling index monitoring cause any performance degradation? Because, even 5% of performance degradation is un acceptable. Please lets us know the pros and cons of enabling index monitoring.
We also planning to enable table monitoring on this schema to collect statistics on table which has STALE statistics. Does this effect the performance?

Thank you in advance

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Best Regards,
Syed Jaffar Hussain
OCP 8i & 9i DBA,
Banque Saudi Fransi,
Saudi Arabia
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