In reviewing drupal 4.6, I noticed that it seems to load most or all the core code and all the modules for all requests, regardless of whether the code is needed. Perhaps the code could be structured to load includes conditionally? Here's my debug list of includes:
DEBUG:
1,056 - /src/drupal-4.6.0/index.php
17,650 - /src/drupal-4.6.0/includes/bootstrap.inc
4,323 - /src/drupal-4.6.0/sites/default/settings.php
9,253 - /src/drupal-4.6.0/includes/database.inc
6,611 - /src/drupal-4.6.0/includes/database.mysql.inc
2,098 - /src/drupal-4.6.0/includes/session.inc
6,097 - /src/drupal-4.6.0/includes/module.inc
60,883 - /src/drupal-4.6.0/includes/common.inc
26,858 - /src/drupal-4.6.0/includes/theme.inc
14,433 - /src/drupal-4.6.0/includes/pager.inc
32,970 - /src/drupal-4.6.0/includes/menu.inc
6,239 - /src/drupal-4.6.0/includes/tablesort.inc
16,937 - /src/drupal-4.6.0/includes/file.inc
30,783 - /src/drupal-4.6.0/includes/xmlrpc.inc
8,394 - /src/drupal-4.6.0/includes/image.inc
49,549 - /src/drupal-4.6.0/modules/aggregator.module
20,653 - /src/drupal-4.6.0/modules/block.module
10,504 - /src/drupal-4.6.0/modules/blog.module
32,514 - /src/drupal-4.6.0/modules/book.module
76,258 - /src/drupal-4.6.0/modules/comment.module
62,976 - /src/drupal-4.6.0/modules/event/event.module
10,496 - /src/drupal-4.6.0/modules/event/event.theme