It is very hard for to beat performance of the MS listbox, especially when offering several features which are not supported by the standard control (for instance, the ability for theming, animation, image in items support, allows for different items to have different height, gradients, etc). Excellent performance is one of our main goals and we are constantly working in this direction. Hopefully we will be able to be very close to the standard control with the next major version.
As to your case, you can accelerate binding using SuspendLayout and ResumeLayout methods like this:
DataView dvCodes = new DataView(_dtCodes, "", "UniqueCode", DataViewRowState.CurrentRows);
radListBox1.DataSource = dvCodes;
radListBox1.DisplayMember = "UniqueCode";
Tell us whether this solution helped to solve the performance issues.
the Telerik team