Indeed, these three operations require three postbacks. The best way to improve the performance in this case would be to ajaxify the control as demonstrated in our online demos.
For your convenience I performed a quick test to check what happens in terms of performance. You can see the results below (also in the attached screenshot)
Request 1: 15.6 kb 393 ms
Request 2: 15.8 kb 422 ms
Request 3: 20.5 kb 432 ms
Total: 51.9 kb for 1.25 sec
for all three requests
Let me know whether ajaxifying the control helps in your case.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed