I have an SJ-410, love it. It goes anywhere, the engine is bullet proof and runs without a care. The side draft carb means it doesn't stall out on hills like a traditional setup.
However, I have replaced the rest of the drive train over to Sammy equipment in order to install parts in it. If you swap in Samurai axles you need to re-weld all the spring pads as your springs are 3" closer together. I max out around 45-50 mph and have troubles going up steep hills in anything higher then 2nd gear. If I was starting over, I would buy a Sammy. I would go with the 410 if you plan on keeping it stock or if you are planning on replacing the drive train anyway. Otherwise go with the 91.