On a sidehill, I've had it at an honest (checked it with angle finder) 30º often. I find that I can actually turn around on hills that are too steep to mow when wet. I go really slow, so a bump doesn't turn into rebounded momentum that throws the COG off the wrong way... over. And over. And over.... as I barrel roll into the holler.
With the added weight up high due to the roll cage I've built, the extra width compliments it with the added stability, and future plans include additional rear wheel weights, just to lower the COG a little more.
Included a pic of some firewood work a week or so ago.