Han -
I'm driving an
L2500 4wd w/ag tires, and my property has plenty of slopes. Sounds like you're referring to side-to-side tilt, and the rule of thumb (conclusion from this board) is that 15 degrees is about the limit of reasonable safety.
Since we first had that discussion, about a year and a half ago, I have purchased a couple of tiltmeters from <A target="_blank" HREF=http://www.tiltmeter.com>R&B Manufacturing</A>, and I can vouch for the fact that 15 degrees is pretty high on my pucker meter.
I've only had it a few degrees past that a couple of times, and both were unintentional incidents. /w3tcompact/icons/blush.gif
Keep in mind that there are other factors that must be taken into consideration besides just the slope. If you're carrying your cutter high, as when you're just transporting it, or if you have a FEL, especially with a load in it, your center of gravity is effectively raised, and you're just that much tippier. Likewise, soil conditions, wet grass, leaves 'n' such can cause you to lose your "footing" and start slipping downhill quite unexpectedly.
And no matter how safe the slope looks, keep that ROPS up and seatbelt fastened.