I've just put a new clutch in the bike even though the clutch in is ok, I'm not sure how many miles I should expect to get out of a new clutch,
I'm debating wether to take the spare clutch I took out with me with the spares.

Average life of an XT600 clutch in the hands of a careful rider is over 40,000km. I have opened clutches on XT's with over 60,000 and the clutch plates (original) are like new.

Just avoid slipping the clutch in tight situations. If you find yourself having to, then you need to look at your gearing.

That's good to know,,,, I do ride hard on occasions but I don't think I will on this trip I want my tyres to last till I get to Canada

If you are travelling light, here is an old trick to get you out of a jam.

Just carry one spare steel and one friction plate. If you manage to burn up the clutch you can just add either one steel or both to the clutch pack.
This will restore function till you can make more permanent repairs.

Thanks actionman that's a good point,

The clutch that's in my Tenere looks as if it has loads of life, I've taken it out and replaced it with a new one for my trip, I'll keep the used one as a replacement for another rebuild