Tommy Fannon answers:
Much less stress on L4 and L5 with sumo if puled right.
Another poster who was forced to make the switch:
MUCH less stress on L4-L5 if you do sumo correctly. To take advantage of sumo, you need to keep your back completely arched. It requires flexibility in your hips and a lot of technique practice. I blew both L4-L5 many years ago... my back was never the same.. i couldn't pull conventional without excessive soreness. With sumo, this doesn't happen for me.
Yes same here, in 2002 i fuct my back ligaments, and still cannot conventional deadlift near what i was then, but i am sumoing more than i was then. speading the hips wide is key and back arch.