We have 257B Caterpillars and run a Bradco 6-1 blade. They are rated for 3-1 side slopes however, we regularly run 2-1's, you can see on the 4th page of our website.
How about bringing a JD out to play up on Mt Helix or Mt Laguna someday? Send your best operator I would love to see for myself what those machines have with someone who was useed to running them. If they are like every other rigid frame machine we have tried, they will walk down the slope while they push. On the plus side, a rigid frame will keep the blade more even, but that's only assuming they would stick to the slope.
You're right about a rear heavy machine in certain respects. That's why you would typically counter weight the blade if the front/back ratio is to far apart. Once you do that, any machine will track better on the side slope application. The way you prove this is take your pallet forks, load a skid full of Keystone, strap it to the gaurd, then drive sideways along any slope. Then try it with the forks empty. You'll be lucky if you don't run a 45° angle to the toe as soon as you engage the drives.
