Chris,
You should always use Dolby. That way, for a program of that length, you can use CBR instead of 2-pass variable, which will cut your encoding time almost in half. You really don’t need variable bit-rate encoding until you get to about 100 mins. in length, in fact, you’ll probably get better quality with CBR encoding. For a 70 min. program, you can encode with a constant bit-rate of around 6.5 as long as you’re doing Dolby audio.