Depends upon at which width you have the rear wheels installed. There are up to four widths between 900 and 1020 mm, depending upon the wheel/hub/spoke configuration. Obviously, the wider the rear track - the greater the safe angle of incline.
John's Tractor will give you an idea of what I'm talking about
as in SIDEWAYS, you can travers 20 degrees depending on wheel width and how SMOOTH it is as well as any impliments you have attached, the PUCKER factor can go UP very fast if you hit a small hole or slip a bit on the front wheels. Over 20 degrees it is anybodys bet. The Jinma (farmpro, nortrac ect) tractors set HIGHER with a lot of ground clearance for going over stumps and such, (remember these are used in rice paddies around the world so water depth can play a factor as well as going OVER the small dikes that hold the water in the fields. ) Higher means less sideways angle traversing but better at going over log/stupm type structure longways.
You can also set the front wheels to different widths too. the backs have 4 different postions I run mine so fronts wide and rears are not, that way rears follow front's rut/path.
I have a 284 Jinma: and with my FEL installed 100% of time, front wheels OUT to WIDE rears are at middle. I go to 15~20 (estimated degrees) with out having too much of a pucker factor but I have come near to getting her over. two times due to ground hog holes ond once due to a bank cave in on the creek. (so now I've practiced up and eliminated over 10 hoggs so far this year) the creek was when I first got property and was clearing over grown multifloral rose / wild rose.
anyhow if you read up on JohnS's web site first you will get LOTS of good info... read it links too if need be and the JINMA maintenance too, (farmpro's are re-badged JINMAS )
I don't think there is any set angle for sideways topple over,,,to many things to consider,,,,its not that great though,,I've had one rear wheel get real light on the side of a hill,,,,best to go up and down,,,,takes a while to get the feel of it,,,after you have went over your ground a few times,safely,,,you can do it again safely,,untill then,you got to be extra carefull,and extra carefull on new ground... thingy