You have 10' of wall to play with too, so why not use it to split a helix into an oval wedding cake version. I.e., a switchback without switches might be possible if you can manage the over/unders .
You are aware of super elevation and proper transitions for 6 driver & longer steam to handle curves or grade changes?
Cable won't work well for hanging without some lateral bracing too IMO. For something static maybe, but the centrifugal forces, especially downhill are gonna cause some sway. (I've strung thousands of cable hangers and rod suspensions in industrial applications. Rod is the way to go imo.
3' at 6" per loop is 6 loops. 72xπ 226.195"÷12 = 18.85' length per loop. Seems steeper than 2.5% offhandedly.
I'd run a 90°/ -l (T) rod/tube brace laterally to both walls and across each dia if possible, cable supporting the vertical. With an oval you'd still have I.D. pop-in ability w/36" reach into 72" curves (-l👈😬👉l-)
If I'm allowed to solder the rails together/ solder a wire tether to hold them/use lionel tubular track clips/, etc. then the T really isn't needed as bad.
