Geoff - The following references are valuable for pursuing AIX performance:

    AIX online documentation:  http://www.rs6000.ibm.com/aix/library
    (AIX, RS/6000) Documentation Library:
       www.rs6000.ibm.com/resource/aix_resource/Pubs/
    RS/6000 SP Product Documentation Library:
       www.rs6000.ibm.com/resource/aix_resource/sp_books/index.html
    AIX 4.3 online documentation:
        www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/aixgen/topnav/topnav.htm
    Performance & Tuning Guide:
        www.rs6000.ibm.com/doc_link/en_US/a_doc_lib/aixbman/prftungd/toc.htm

There are the usual Unix performance checking commands, plus various public 
domain
things like the 'monitor' command, 'lsof', etc.

The various *SM and AIX redbooks supplement the lot, and can lend guidance
as to judging performance.  The biggest factor is giving the system lots of
real memory (which unfortunately is rather expensive on "commercial" systems).

   Richard Sims, BU