How fast Video Transcoding can be with CUDA?

I need a exact illustration to indicate how fast video transcoding can be with CUDA? If the result is favorable, maybe i will update my laptop GPU to GeForce GTX 580M. :) Nvidia claims it is with up to 384 CUDA cores and up to 2GB of 256-bit GDDR5 memory is it. Sure the main purpose of this laptop is for gaming, but I also need to use it to video transcode regarding my tons of Canon HG10 shootings. Please guide me where can I find the answer?