I need suggestions to improve speed and usability. I have a RadComboBox with over 700 items. The user needs to be able to select multiple items from the list, so I have checkboxes turned on. However, the combination of checkboxes and a large number of items makes the combobox open and close very slowly. I was told that the usability is not acceptable for the users and I need to make it work faster. I have 5 of these long checkbox lists on the page.