I think in the Cub owner's manual, it tells you to not mow across any more that a 15* slope. I mow three different yards with a Cyclops and a lot of the three yards have slopes that are at least twice that steep. Have I checked the slope degrees for accuracy? No, but to quantify the steepness, if you don't get on the fender, you can't stay in the seat. Also, if the grass is damp, the tractor will sometimes scoot downhill while mowing across a steep slope. That defines how steep it is.
I have also mowed going up the slope to the point that the front wheels came off the ground on an 1864. Same slope with 1862, that doesn't happen because I guess the Magnum engine is heavier than the Command?
All cases above are with turf tires, not ags.
PS. I'm not advising the OP or ANYONE to do what I do, just that that is my experience. If you buy the Cyclops in the CL ad, you'll throw the rest of your grass cutting stuff away. Too bad though it's not an 1864 though.
PSS. My opinion could be biased as I've never tried the Gravely being shown here. Don't think I want to.