If you want to run a report that will show you the top spending clients for your practice, the Client Report will provide that information using the following settings.
For the date range filter, you will only want to use the filter for "Amount Spent Date Range". Enter your starting and ending dates.
Click on Generate and the report will be created. It will display all of your clients based on the amount spent, highest to lowest. You can then export it to Excel and filter on the number of clients to get the top 100, 200, etc.