How would it be with a 50 lbs bob trailer. I have never really ever though about miles and elevation like a 6% grade or a 9% grade. All I know for sure is that if you look to the top of the hill or mountain you have already defeated yourself. When climbing a mountain or hill never look more then 8 feet in front of the bike or it's twice as hard. Try it! climb a hill or mountain with out looking long then 6-8 feet in front of you and you will notice it's just a little more strain then riding on flat land but if you look to the top, you might as well try to drag a bull elephant up that hill with you cause it's really going to feel like you did.
Sometimes you just don't ever know until you try. Tell me what you think.

If this works for you then don't look more than 8 feet in front you . Heck if you close your eyes it might feel like you're actually going downhill Here's a calculator to figure the grade
Grade Percent Incline And Downgrade Calculator