The only way to increase the encoding rate for WMV is using an add-on encoding card. We use the ones from Digital Rapids. They are not cheap, but if you have a lot of content you need to turn around quickly they are worth it. You can see them at

http://www.digital-rapids.com/Produc...RC-Stream.aspx

You can encode multiple bit-rate files all at the same time and can get 3x to 15x encoding rates based on the card you buy.