I don't think you should worry too much about an extra 5 to 8% on the load. However, you know your bike far better than we can, and the trip might be quite committing and serious on those isolated roads. Is there a reason you are worried? Did you feel you were at the limit on previous trips?

I have to say I'm with nubcake on the suspension stem, but if you like it then it's not a problem, the extra weight wont have the slightest effect on the stem.