System Stats opinions Please - WORKLOAD vs. NOWORKLOAD?

Bit of a background - We've a big (10TB) 10.2.0.5, 5 node RAC system for a big Oracle eBusiness Suite (R12 - HRMS/Payroll) implementation and at the minute we are running on some old (2 years old) gathered NOWORKLOAD system stats and since then a significant underlying IO infrastructure change has gone in and we are planning to upgrade the underlying server infrastructure from IBM P5 to IBM P7 soon as well (which introduces significant CPU changes etc.) and me personally think its the time to let Oracle know about all these changes under the carpet by updating the System Stats and since its likely going to be a significant change as potentially all the plans will be impacted (and few/some might go in an unintended direction) so want to know your opinion on these questions about it please :

1. Shall we just update the Noworkload Stats and leave it as it is (db_file_multiblock_read_count in left unset i.e. left for the system to set automatically). OR
2. Shall we go for the WORKLOAD stats instead? If we go this way then I am planning to go by the brilliant strategy mentioned by Christian Antognini in his lovely book 'Troubleshooting Oracle Performance' for stability point of view.
3. We are planning to go 11g (11.2.0.2+) in the 2nd half to next year as well - is better to leave this evil till then if 11g introduces or improves the system stats mechanism significantly? An opinion favoring this is also that we'll get better and more robust testings done if we pile it on 11g project so may be a bit safer approach (and better for work/human resources planning as well).

Out of the 5 RAC nodes, 2 are dedicated to OLTP stuff, 2 for Batch (Payrolls etc.) and 1 for (low priority) Reporting so obviously there are concerns around getting to a setting that's going to be the best fit for all of them and since thats not easy to achieve the risk is higher.

I am sure I am not new here and some of you'd have come across these questions as well so am wondering if I can get some opinions or advices please? Particularly from the people who have gone from NOWORKLOAD to WORKLOAD (preferable eBusiness suite and even better HRMS/Payroll) please and also from the people who've distributed workload like we have on difference RAC nodes- if they can share their experiences on how did it go for them - that'll be good please? (Obviously everyone's system is different and so is everyone's workload but if 8 out 10 say its been good for them or even bad - then that gives a bit of a feel about it). Or are most people still running on 'safer' NOWROKLAOD stats please becs WORKLOAD is deemed to be a bigger change?

Also, in the end - I've heard some not so great stuff about IBM P7 as well - just wondering if there are people out there with some experience on these as well please?

Thanks in advance.

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