The question totally depends on your setup and what you're carrying.
For front/rear, it's tough to say what you have in the loader and if you have a BH mounted. You being in 4WD or not makes a big difference on your safety zone.
For side/side, that is tough to say as well. I feel 100% more comfortable on slopes without the FEL mounted and with the MMM mounted because of the dramatic shift in COG. Furthermore, I only go one way around a particular slope because of the extra weight the OEM bagger has on the right side...can't hit the same slope going the other way.
Then there's the time my Stepdad had a 400# load of timber in the loader and while I wasn't looking felt compelled to raise it several feet. Don't ask me why. One wheel in soft ground and the thing tipped right over.
There really is no answer for your question. It is based simply on the comfort level of the operator and the given situation. I saw a picture one guy posted of him on, in his opinion, a wicked slope. I hit slopes 3 times as steep (approaching 30 degrees) sideways every time I mow. Of course, I go slow and careful. And I thoroughly checked all my yard's slopes on and off the tractor using the 'rear tire lift test' before working.
Then there was the 500# of play sand in the loader yesterday. With the load skipping 2" above the ground couldn't go on a very mild sideways slope without losing my fortitude and choosing another direction.
Not trying to be blunt or anything, but I would not encourage anyone to have a table of acceptable slopes for different configurations/situations. It really needs to be a "seat of the pants" thing. Every moment on the tractor is different from the next. That's why I wear my seatbelt 99.78% of the time.