"I'm on a small B2400 which is fairly narrow"
My 670 was fairly narrow too. Had bar-turfs which are pretty wide for a tractor tire.
Even after a couple years, I always felt the tractor was lacking stability on even a mild side slopes. I even parked it one day on a slope the was slightly in excess of 15°. Got off the tractor and gave the ROPS a pretty good shake. Didn't budge at all (now, what would I have done if the tractor had rolled?? Obviously, once my embarassment subsided, I'd use the pick up to right it.). The rear tires were loaded and I got another good lesson in inertia that day). Ol' Bird did this too...guess that's where I got the idea!
Even though my 790 is quite a bit taller then the 670 was (6 to 8" at the seat, I'd guess), with those bigger loaded tires (R-4's) carry considerably more weight.
When the 790 was delivered, the salesman drove it across the same slope I was just discussing...he went a lot faster then I've ever driven that slope! And, it was raining hard at that time (not hard enough to keep me off the seat for a test of all the hydraulics and how it pulled though...sure did get soaked right through though!). However, he had no qualms abouyt that slope. One of two things...he either has enough experience to know the capabilities of his tractors..or, complacentcy reared it's ughly head and we were just lucky that day.
Anyway, just an anecdote...our tractors are probably more stable then we are...but it's sures feels spooky on a side slope!