I have a Winforms app in which there is a "client" drop-down implemented as a UltraComboEditor. For most users, who are assigned to a specific office, this will have a few dozen entries, and everything is fine. For highly priviledged users, such as those working at the company HQ, every client in the system is available, however. This is on the order of tens of thousands of entries. If I bind this list to a plain Windows.Forms.ComboBox, it remains responsive and usable. The performance of an UltraComboEditor bound to the same list is unacceptable, however. Clicking the drop-down arrow results in a 5-10 second delay, and scrolling is unusable.

Is there anything that I can do to help the performance of the drop-down. Changing to another control isn't really an option, since the highly-priviledged users are a definite minority, and I don't want to break the application for the vast majority of users in order to satisfy just a few. I can't get the plain windows forms combo to match the surrounding UltraComboEditors style-wise, either.

I have tried binding the drop-downs to a List<KeyValuePair<int, string>> thinking that smaller objects might help, but it has made no appreciable difference in the performance of the control. Here is a snippet in which I bind both drop-downs.

            clientComboBox.AutoCompleteMode = Infragistics.Win.AutoCompleteMode.Suggest;
            clientComboBox.AutoSuggestFilterMode = AutoSuggestFilterMode.Contains;
            clientComboBox.DisplayMember = "Value";
            clientComboBox.ValueMember = "Key";
            clientComboBox.LimitToList = true;

            comboBox1.BackColor = clientComboBox.BackColor;
            comboBox1.FlatStyle = FlatStyle.Flat;
            comboBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
            comboBox1.DisplayMember = "Value";
            comboBox1.ValueMember = "Key";
            comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;

            var list = clientLevelSummaries.ToList();
            list.Insert(0, new KeyValuePair<int, string>(0, " "));
            clientComboBox.DataSource = list;
            comboBox1.DataSource = list;

Is there anything left to try, other than having one control that looks out of place?