The ultimate hill approach IMHO, ignoring minimum speed concerns for a moment, is to use the extra load on the climb to get to the best bsfc spot. i.e. find the best compromise between 75% load and 2500rpm if your bsfc map looks like the following (manual trans assumed). And then kill the engine near the top of the climb so that you barely coast over the top and down the other side.
Note, efficiency tapers off more gradually to the "west" or the "southwest", so that is the side I would error on if possible.