I am a dutch biker, done lots of touring both on and off road, using panniers back and rear and a BOB. I did part of the GDMT last summer, great fun. Touring needs strong wheels! I had problems wth panniers and rear wheels. For me a strong rim and at least 32 or 36 spokes crossed over 3 work well. 20-25 lbs sounds awfull light fot the Great Divide! There are several stretches where you'll need food for a couple of days. Are you sure you can stay this light? The handling of a bike is seriously effected by panniers, worse if you pack everything on a rear rack alone. A heavy handlebar bag is bad for steering and you loose some sight of the road. I used my BOB on the Great Divide and I find that it handles very well off-road. It is a lot heavier than a pannier set-up though. Anyway, have fun!