I'm at about 244:1 in double low, 1st gear.
4.30st gear, x 4.7 x 2.28 X 5.29 = 243.7
My 3.0V6 (3vze) will also idle at 300 RPM. Just kinda wheezes along.
It is funny when you climb a rock, and the RPMs drop under 300, the dash floods with warning lights, but then the tire goes back down the other side and the revs come back up. Technically, I don't think the engine is "running" for a couple of seconds, but it is still turning over!
100:1 Makes the trails a lot easier. You can drive more smoothly. You can climb and descend rocks that you used to bounce over at 50:1.
As noted above, 100:1 means you are about 1/2 as fast as the majority of a group trail-ride. You wind up in 3rd or 4th gear on the trail, but you drop down to 1st and enjoy the lower gears at the rough spots like rock gardens, ledges and big climbs.
I find that wheeling with the club I'm in about 50:1 most of the time with 36 inch tires.
Above 200:1 is silly slow and can actually be a bad thing. Your wheels are all but stopped. No momentum to carry you over an obstacle you can't crawl. On ice, going slowly is one thing, but you might as well lock 'em up at 240:1. No control. Descending something sketchy is also a problem. You can't get enough tire speed to do anything if it starts to endo.
Having the CHOICE to go silly slow is really nice though. I often use the 244:1 ratio on the tough trails. but when the going gets REALLY tough I end up in 2nd or 3rd gear, double down(2.28*4.7), engine at 5K. That is about 100:1. I like to descend big ledges double down in 2nd. Right where you are looking.
I would say in summary that 100:1ish makes the rough parts of trails 2x easier/safer. It is also about perfect for tough obstacles that require tire spinning action.