If your ultimate destination is DVD, then use a CBR of 8,000,000 for anything less than 70 min. long.
Longer than that and you need to use a bitrate calculator and get the VBR settings from there.
My personal favourite is the one found at
http://www.johncline.com/bitcalc110.zip
I would also do this as a 2-pass encode (render) simply because it will help to maximize quality.