The conventional wisdom, which I subscribe to, is go with the minimum grade possible in your situation.
I actually was looking to go for 2% or less, but given the space constraints, the grade easements at the start and end, I ended up with 2.4% and 2.5%. Still very manageable, but smaller locomotives with a larger consist sometimes can have minor issues. I know the little Legacy S7 has a problem with a bunch of Menard's boxcars. They're not the lightest rolling cars, and the friction and the grade were a challenge for the little S7. Including the easements, my grades are over 22 feet long, that's all the space I had to make them work, so they ended up being a bit more than the 2% goal.
