Sorry I'm so dadgum late..didn't see your post.
We run 3" straps mostly, which are rated at 20K. Not so much that 4 straps on a tractor wont exceed the load potential, but the wear and tear, dirt, grease, oil, Blueberry gorp, and sunlight degredation on straps lowers the real capcity of the things. Like you, I shudder at the thought of something coming off the trailer.
The 2" 10,000lb jobbies ain't bad for GP and should do fine for occaisional use. If you plan on using them often, and with mud and crud as a constant, it dosn't hurt to add a little overkill. The failures I have seen other guys have, seem to always be worn 2" straps and Ratchetts that have busted pawls. If you have 4, I reckon you would have to be going pretty fast and come to a instant complete halt in order to bust all of 'em at once, I just like having the extra insurance.
Hope this helps!
Stay safe!
Dingeryote