Jonny, I've got a Maxxis Ardent on the rear of the Zero and it is a very fast rolling tyre - not the greatest grip when putting the power down on a techy climb but it's swings and roundabouts, innit? I like it though as it is very predictable, you know when it is about to 'give' which is good.
I still think the best out and out compromise tyre I've had though are Nobby Nics front and rear - grip and fast rolling - but the Gatestar 4x evo snakeskins, not the Godawful cheap and shoite performance lines.
Out and out fastest tyres I've had are the Racing Ralphs, fast and light but the grip in any kind of wet was so bad I had to dump them - truly awful unless you are just doing fire roads, in my experience.
They're going to be for fast, long distance XC riding, I have Ardent and Ardent Race on my Whyte and love them. I'm not too bothered about big, nobbly tyres. If I'm doing major off road riding I'll use the main bike. Weight and fasty rolling are the main things I want.