Depends on the setup. My machine (exceedingly similar to a
BX24) can handle what I would call a 30 degree slope before I personally don't go any futher, but that is without FEL and BH and with MMM and Bagger. I would go UP similar without a full load in the bagger (too rear-heavy...wants to pop front wheels in the air) and DOWN similar with 4WD engaged (braking in front wheels)
The attached pictures demonstrate the steepest part of my yard and about the limit of slope on which I feel comfortable on my machine. If I go STRAIGHT UP this slope with a full bagger, I can "skip" the front wheels on the ground with delicate treadle control. Going down isn't a problem.
With FEL and BH (no MMM), I don't feel comfortable going much steeper than, say 20 degrees. And that's probably pushing it. The COG is much higher with the FEL and BH installed.
Same deal with up and down, but it is amplified with a load in the FEL. From personal experience, it is NO JOKE to have 400+# of soil in the FEL bucket and lose traction on the rear wheels, sending you down the hill without complete control.
I would NOT consider putting my tractor, FEL AND BH installed, on the slope shown in the attached pictures. I carefully traverse up and down the slope, however, without any problem.
I have actually traversed a hill downward, backward, to make handling a heavy FEL load safer in particular instances. Generally speaking, though, I feel comfortable with 4WD going up and down most any slope.