Option 03 · Recommended
The only arrangement where every clearance passes and neither machine's working zone touches the other's.
Dashed outline = minimum clearance envelope, 24" each side and 36" in front · shaded = working zones · stair wall at left
Side clearance of 100" toward the stairs and 44" toward the back wall, both past the 36" preferred figure. Front clearance of 83", which covers the full 80" of cable travel. Run-off of 116" behind the belt. The treadmill's run-off lane and the trainer's working envelope share no floor at all, which no other pairing on this list manages.
Your treadmill is 38" wide and the wall stub to the left of the stairs is 38". Pushed into that corner, the machine's outer edge lands flush with the edge of the stair opening. No leftover sliver, and the 53" doorway stays completely unobstructed.
The console has to sit at the stair-wall end so the belt runs toward the back of the room. That gives 116" of run-off and means a stumble carries you away from the stairwell. Flip the console to the back-wall end and run-off drops to zero.
You run facing the darkest wall with every window behind you. Whether that matters comes down to where the wall-mounted TV sits: if it is visible from the near corner, you have traded a window for a screen. The console also ends up adjacent to the step-down, worth looking at in person even though backward falls are the realistic failure mode and those carry you the other way.
The trainer's position along that 199" wall is the one adjustable variable, and you have room to move it. Centering it on the wall gives 72" on each side. Sliding it toward the back wall buys distance from the treadmill. Where you land depends on the side window, which needs measuring.
The outlet you use today is at the far end of the room. Treadmills should not run on extension cords, so this placement most likely means adding an outlet near the near corner.