Cuda with TMPGEnc 4.0 Xpress

Hi i just got a GTX 260 Core 216 yesterday. I read that with Cuda it boost encoding. But i did check option to Enable Nvidia Cuda 2.0. And honestly there no change at all my cpu use still around 90% and there is no speed change from encoding divx to mpg2 or dvd to divx with cuda and without cuda. MAybe someone have an other experience with it ?