I use Freemake regularly to convert mp4 and avi to wmv.
I just checked and got this result: An mp4 of 540 MB in size and 35 minutes in length takes 18 minutes to convert to WMV.
That equates to about .9 GB per hour for this particular mp4---it's 960 x 544.
I have an i-5 2500 with 4 MB of RAM.
You don't mention the size or file formats of what you are converting.
How do my figures compare to yours--in terms of GB per hour?
If you are converting 20 or 30 or 40 GB of material, you may just have to wait.
As far as I know, I am just using default settings.