Did you ever compared client-side RIA frameworks? Alexey Gavrilov  has written a great test to directly compare performance : Silverlight (WPF/e) vs. DHTML vs. Flash (Flex) vs. WPF vs Apollo vs. Java (Swing):
"The goal of this test is to directly compare performance of different RIA frameworks / approaches in different browsers. The test, which implements simple 2D animation demo, was initially created in DHTML, then ported to Silverlight (WPF/e), Flex and WPF (XBAP). The code used in DHTML, Silverlight (WPF/e) and Flex is essentially the same while for XBAP demo it was ported to C#."