I typically fly at 250-260 and no more than 300. If I have to fly that high for battery purposes I just concede to running two batteries. That usually means a pretty big site so sometimes I have to have two separate flights to maintain visual contact. The reasoning for lower altitude is a lower angle of attack and better resolution. If you are trying to hit the bottom and middle of the wall you will have to be further away from the subject if you are flying high which decreases resolution as well.
I know you will be told that the more overlap the better, but I am getting pretty amazing results with 65 side/70 front. I would try perpendicular to the building faces if conditions allow. I haven't had much luck with the 3D mode yet, but that's definitely the way to go if it works for you. I don't use it primarily because I use Ground Control Points and I am not getting as good of accuracies with oblique images. Not bad grade, just not sub-centimeter.