Like they all are saying, it's going to vary from event to event, and trail to trail. Here's something I copied from our club's newsletter:
Trail Rating Guides
Moab Jeep Safari Rating Guide:
1- All weather road; 4WD not needed.
1.5- Graded road; 4WD may be needed in poor weather.
2- Unimproved or rarely graded road. 4WD or extra clearance needed at times, with no special driving skills required.
2.5- Road rarely maintained, 4WD, good clearance, low gears often needed, with some extra care and a bit of driving experience useful.
3- Road in difficult terrain, rarely maintained, 4WD, good clearance, and low gears essential, with some driving skill and daring required.
3.5- Road in difficult terrain, probably maintained only by occasional users. Excellent stock truck or utility vehicle required, with considerable driving skill and daring needed.
4- Trail either never bladed or badly eroded. Stock vehicles are in jeopardy. Modifications for improved off-road performance and top driving skills needed.
(Original description written a few years ago by Jack Bickers: "with driving by World Class Yahoo Jeepers not much concerned with vehicle durability or personal safety." It is common to have as many as 10% of the vehicles experience major mechanical failures (gears, axles, driveshafts) on these trails.)
Trail Ratings for Jeep Jamborees:
Every Jamboree trail is rated from 1 to 10, based on the overall trail, not just on one or two tough spots. Rain can increase ratings by 1-2 points. Tow hooks required on all trails.
• 1-3: Obstacles that are easy to navigate. In optimum weather conditions, some of these trails may not require the continual use of four-wheel drive (4WD).
• 4-7: Moderately demanding trails on which 4WD is required. You may encounter a variety of challenges, including mudholes, boulders, and stream crossings, on the trail.
• 8-9: The likelihood of getting stuck is considerably higher. Mud holes here may be deep and rock climbing will be more arduous.
• 10: Reserved for the most demanding off-road trip in the country-the Rubicon Trail.
And here in Indiana we have the Badlands (Attica) Rating Guide:
Green trail: Moderate. Tow Hooks required.
Orange trail: Tough. Lockers and winch suggested. Possible body damage.
Pink trail: Extreme! Lockers and winch required. Body damage likely.
If it weren't for the trip home, the cost of repairs, and the nagging from my wife, ...Heck, I'd try 'em all!
Keep on Jeepin'
Scott