<font color="blue"> would it not make more sense to go with a lighter machine, and
ballast the heck out of it, on the premise that the ballast will lower the center of gravity overall </font>
I have a Kubota B2910 and did just that. It has about 350# of iron on the underside of it, the rear tires are filled too. I still only use it to go straight up & down the slope.
I also have a NH TC24D, but left that bare, no fluid fill, only rear wieght is the weight box or an implement. I do have 100# of wheel weight on the FRONT wheels to hold the front down when the FEL is off and a heavy implement like my snowblower is on the rear . . . but I don't use the blower on my slopes. Just like the B2910, I only use the TC24 to go up and down, it does all its work on the upper ridge or in the valley area, none on the slopes.
I agree about 100% with what Henro wrote in his last post.
Regarding the post by Tracdoc (related to the PT on the slope), unless he has the weight transfer system to move the weight onto the wheels and off of the implement, then he won't experience the stability I was referring to. Their weight transfer system was NOT available on the PT425 when I looked at them, I believe it was not available below 30hp. Ventrac has the weight transfer system standard on the 3000 and the 4200 series machines, but not the 4100 (it is optional on that model). If I recall, Steiner had the weight transfer as standard (when I looked at them, not sure if it is still true) on all their models except the 230, it was not available for the 230 but that is only a 2wd tractor so it wouldn't make sense.