I had noticed that our internal dashboards were getting slower and incorrectly assumed that it was the amount of data. Sadek investigated the issue and found out that it is actually caused by the control to add new graphs to the dashboards. This has been fixed in 5.0. For those of you on 4.5.x, there is a workaround.

Thanks Sadek.

Workaround:
in ./modules/Dashboard/index.php
Comment out the following lines (all instances of them in the file)

PHP Code:
$report_def = $json->decode(html_entity_decode($saved_report->content));
...
...
if ( empty($report_def['chart_type']) || $report_def['chart_type'] == 'none' ) {
     continue;
} 
This will, however, display all summation reports in the "Add a Chart"
dropdown, including those without charts. It is not harmful if someone were to select a report with no chart. It simply doesn't display anything except for the title bar when added.

For sugar instances with a large number of reports, this will bring the response time down from 50+ seconds to approximately 2 seconds.

For more information as to why this is happening, please see the bug description.

Best
Sadek