InfoPath Dev

 It sounds complicated and I think you may need a developer - but maybe you should skip using InfoPath altogether and get the developed to write something to load straight into SharePoint....

Is the slow performance caused by using rich text boxes ? If so could you switch to text boxes?

 I assume that you could save the excel data in csv or XML format - I guess you could write code to then import the data into the form on the form_load event - another approach might be to cut and paste.  What type of form is it - is it browser based? 

 I have found (with browser forms), that on_changed events can get generated (with the data at the time that the event was kicked off), but the event does not actually run until later  e.g. a button click.  I think your code may be conflicting with the rule execution.  As a result of the above, my conclusion is that the safe ...