Let me be sure I understand...4 track from end to end? More or less continuous grade from end to end? Continuous running or point to point was a little unclear???
Your stated concern deals with height between levels. I am assuming basically one run or set of track between"stacked" terminals (joined at the "dogbone" for return to the "other" level?
I suppose one way to determine the separation of levels is to simply build a 6ft experiment. Put a "shelf" at what you think is the comfortable low height and the same for the top level and see if that makes for comfortable viewing. Place some track and rolling stock and structures. Reach in to couple or uncouple or to throw turnouts...still comfy, then go with those heights...or adjust as needed.
However, instead of one long continuous climb or downgrade run...consider helixes.
You mentioned a "dog bone"...well two helix, back to back along one wall with your proposed peninsula that could be a branchline on one level and perhaps a mega factory or port or other industrial district or terminal yard for passenger trains on the other level thus giving you top to bottom to top again via the two helix and industrial switching without affecting the thru trains.
You could use the helix as a means to continuous run and you could, if you elected, use one or two of the tracks as "hidden staging".
The helix would need to be very large to hold four tracks going up and a second helix with four tracks coming down.
Let's see this in our minds (swirling mist...clearing...now) the train comes out of the overpass (hiding Helix 1) on the North wall heading right to left into the large city that is also the division point. As a thru fast freight, it has no work so it simply slows for a crew change and takes off curving onto the West wall and thru the outskirts of the large city into the suburbs and eventually (curing onto the South wall) the rural country beyond. As the fast freight passes thru the small farm town, it begins the curve onto the East wall passing thru hills and some small spurs leading to coal loading tipples of small mines. The freight makes the next curve onto the North wall again and we can see thru the hills that the train enters a tunnel. (several minutes pass as the train gains height in the mountains where we cannot keep up with it on the road...as the train actually goes up Helix 2)...SUDDNELY, at the top of Helix 2, the train emerges on the North wall going left to right via a tunnel (perhaps the same one or one miles away?) and immediately crosses a large river on a steel truss bridge before curving onto the East wall and running across the river bottom with large crop fields. Passing thru a small town with a couple of grain elevators (perhaps one older wooden elevator and one newer concrete elevator), now the train curves along the South wall and passes thru a small town with a couple of manufacturing shops and crosses a couple of streams as it cirves around the next corner into the next disivision point where there is work to be done...cars added, cars pulled and fueling with a new set of engines, caboose and new crew. The fast frieght waits as the branchline local comes into the yard, and then the fast freight whistles off rounding the next curve onto the north wall passing behind that large factory and disappearing from sight into Helix 1.
Obviously, a helix needs to be large enough to hold the owner inside the center of the helix. Personally, I would suggest nothing smaller than 72 inches. The grade is another factor that will help determine the distance between the lower level and upper level. Personally, I would not accept anything less than 24 inches...but at the same time...I like to "operate" meaning industrial switching, thus I need to be comfortable spotting cars or picking up loaded cars at various industries and switching the cars onto or from the thru freights.
Perhaps the lower level would be around 29 inches (around the ehight of a standard desk) with a couple of swivel office chairs at the division point, one for the local operator/switch crew and one for the thru freight operator for any switching he must do...perhaps a swivel chair at the two other walls for any local switching...thru freights could be operated while standing and walking with your train. Upper level around 53-54 inches. (My layout is "arm pit height" at 53 inches so I can reach in 30 inches from edge of bench to the wall. Your personal height may adjust that a few inches.)
Regardless, your idea is certainly a goal that you can reach whether a continuous visible run from lower to upper...or level running with a hidden helix or even two helix. It is all part of the fun and challenge of O Gauge Railroading.
