More important than the absolute steepness of the driveway, of course, is how sudden the transition is.
I agree with carringb that doing a slow, careful trial run before making any modifications is only sensible. I would tend to advise against a significant lift (and I think 5-6 inches is pretty significant), if only because it will make getting the RV level at most campsites very difficult. You'd have to put 5-6 inches of ramps or other lifting under the front to get level on a dead level campsite, and that's a lot of ramps or blocks or jack extension.
If you only need an inch or so, air helper springs might give sufficient clearance without any real suspension changes.
