When converting a non-trivial Sitecore 4 solution to V5, consider switching off the search indexes in Sitecore. It should help to speed up the process quite a bit.

update: removing item:save event handlers might also save you some time:

<event name="item:saved">
  <handler type="Sitecore.Links.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
  <handler type="Sitecore.Tasks.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
  <handler type="Sitecore.Globalization.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
  <handler type="Sitecore.Data.Indexing.ItemEventHandler, Sitecore.Kernel" method="OnItemSaved"/>
</event>

although out of these standard four, the first one is more likely to produce some impact, if you've already switched off indexing.

Unless you are running conversion on top of already existing items in V5 database, there's no need to look into item deletion. Saving an item, on the other hand, happens quite a few times.

Once you feel that you're getting close to the desired result, you can use Control Panel in Sitecore to rebuild link database and search indexes, to restore the standard functionality.