How to Enable unity with webcam efficently

Recently, i have done some work on the unity for webcam use.
i achieved using webcam, but not realtime.
My webcam is logitech which can reach 30fps @ 640*480 resolution.
but my program shows that the fps is only about 20.

i also test the elapsed time of function(tex.apply()), its about 40 ms.
so can anyone help me with the speed problem?

PS:
I have read the following link, and using improved methods.
http://forum.unity3d.com/threads/30817-UnityAR-ARToolkit-Interface

My platform is

  1. Unity3d 3.3 Pro
  2. Nvidia GTS 450
  3. Logitech webcam
  4. i5-2300*4 core

You can use the new Unity 3.5 public beta which supports WebCamTextures checkout: Unity Video Remake: Webcam Textures - iKriz.nl for a basic script