Not a fair question if your other platforms have full time Database Administrators.

Any operating system or database that you choose will not perform optimally if it is neglected. If you are not monitoring and analyzing database tuning information on a regular basis on your iSeries servers, you've answered your own question. All databases need tuning. Permanent access paths, indexes or logical views are needed for all databases for data to be retrieved, updated and/or deleted in an efficient manner. Use the IBM Database Monitor commands, use our Query Optimizer or use a 3rd party tool. If you want the iSeries to perform
well and win the performance comparisons, give it an equal playing field.