hmm. I don't think we'll get much from RTI ramp info on 4x4's - those numbers are about flex across a frame vs. wheelbase. A long wheelbase vehicle will tend to have worse RTI index, other things being equal. RTI is not relevant to trailers - as mentioned, at low speeds, trailers will no suspension have great RTI numbers.
We can't be worrying about how well a trailer will tilt on a ramp. We can worry how well the suspension will hold up on dirt roads, with pot holes, at 45 mph - and leaf suspension USUALLY will hold up well ....
However - it will USUALLY transmit more jolts/bumps/vibration to your trailer. Your cups and saucers will bounce around more, you beer may be fizzier.
It's a matter of unsprung weight AND your springs AND your shock valving, assuming you have shocks. Bigger tires help BUT increase unsprung weight - you can over do big tires.
I have pics of failed leaf suspensions - one a rear Bronco spring that that snapped - one a heavily built off-road trailer behind a Rover (with coil springs on solid axle..... ) - both vehicles required welding to repair in the field ( the trailer repairs happened a couple more times for the Wolf Expedition but to be fair he isn't a mechanic, and depended on 3rd World repairs each time ).
Adventure Trailers found that the rubber torsion spring suspensions failed with dust getting in them - but what failures have been seen with the newer design trailing arm, with air bags or leaf springs? Does anyone have experience or heard of them cracking welds or something?
I don't think repair when broken is a good reason to go with one design either - I would hope you build or buy with the idea that it will hold up for the application.
Paul, the ones you have seen failed - what type? Rubber torsion? Or?