J.T.:
In the real world of ops engineering we use the topo to figure out where the difficult bits might be and then, if it is really critical, a couple of fine chaps/chapesses draw the short straw and have a fun day out in the bush with a theodolite and associated kit.
That is often the only way to sort it all out.
Alas, a popular performance vendor in the U.S. is not even using topos, rather the data derived from the Space Shuttle mission. I have those data as an adjunct on my GIS program. Fairly good for planning, but that is about it. The U.S. 1:24000 topos are generally good (excluding Alaska) but still need at least a Day VFR flight inspection.
It isn't happening with some exceptions.
Also, pilots seem quite confused about visual avoidance providing an "out." OEI flight paths are weather independent as you well know. If they must be flown it is all the same, DAY VFR, Day IMC, etc.