Что может быть лучше чем поставить IBM AIX на IMB-сервер.

Посмотри ссылку :Linux, Windows - преимущества и недостатки систем

Там таблица есть сравнения. Из неё очевидно, что самые важные параметры касающиеся именно работы БД Oracle наиболее высокие у Unix. Если IBM AIX можно отнести в данном случае к Unix, как коммерческую ОС, то я бы посоветовал её.

Вот список параметров по Windows, Linux, Unix:
авторPERFORMANCE(OVERALL) 4 7 9
Performance (Online Transaction Processing) 7 8 9
Performance (Decision Support) 6 7 9
RELIABILITY 7 7 9
Security 3 7 8
Scalability 7 7 9
Vendor Support 7 6 9

Про методику не в курсе.

to Apex:
Я могу кинуть файл, в котором были эти сравнительные оценки. В крайнем случае можете на него сослаться. Документ вроде серьёзный: OCP Instructors Guide for Oracle DBA Certification. A Study Guide to Advanced Oracle Certified Professional Database Administration Techniques

About the Author
Christopher Foot has been involved in
database management for over 16
years, serving as a database
administrator, database architect,
trainer, speaker, and writer. Currently,
he is employed as Senior Database
Architect and Senior Oracle Instructor
at Contemporary Technologies, Inc. in
Pittsburgh, PA.
Chris began his career working as a
database administrator at Mellon Bank. For ten years at Mellon,
Chris served as a DBA and later as the bank’s Client Server
Systems Architect. During his tenure at Mellon, Chris was
responsible for helping to create Mellon’s support
infrastructure for all non-mainframe database applications. As
a result, Mellon was asked by the Oracle Corporation to
participate in Oracle’s Showcase Environment program in
August of 1996.
He broadened his skills at Alcoa, learning the world of
manufacturing and became Alcoa’s Database and Server
Architect in April 1998. Chris was responsible for database and
hardware server strategies at a corporate level, reporting to
Alcoa’s Chief Technology Officer (CTO) and Chief
Information Officer (CIO).
Chris is the author of over twenty articles for a variety of
magazines including DBAZine, Database Programming &
Design, The Data Administration Newsletter, and Edge- The
Database Survival Guide.