I used to use Google Maps Directions a lot on my everyday older computer, the beauty being that you could play "what if" games with alternate routes by simply dragging the route around to experiment with distances. Unfortunately, Google disabled this feature, now telling me I needed a newer operating system on my Mac, and on the iPad I seem not to have the versatility I once had - maybe I need to play with it more.
RobbW, to answer your question, for the short distances we usually drive in the i-MiEV, it's an exercise that's perhaps more trouble than it's worth. I don't know of any such nav tool.
That feature with the variables you mentioned, as well as altitude change, wind direction and speed, traffic conditions, ambient temperature, etc. I suspect could be thrown into a massive algorithm by a BEV manufacturer to provide a custom and presumably more-accurate Range Remaining display as well as trip route optimization. Even the first Leafs gave you warning if you've programmed in your destination and you aren't going to make it. Lots of room for development and I'm sure it's being refined constantly. Hmm, good excuse to stop by a Tesla store and see what they have nowadays.
I'm just fine with our i-MiEV's simplistic RR display using (we think) the known algorithm based upon how/where we drove the last 15 miles, with the RR display roughly compensating 10% for aircon and 20% heater. I find myself mentally compensating for speed and altitude differences (and sometimes headwinds) - RR hasn't failed to get us to our destination 'safely' in over 50K i-MiEV miles of driving. For longer trips, having the older Garmin show DTG in a large numeric provides a wonderful counterpoint to RR as we drive.