I was a conventional deadlifter until about a year ago. I was very weak off the floor but strong at lockout. I switched to sumo and was strong off the floor, and weaker at lockout, but my max sumo was about 50 pounds higher than conventional and has steadily improved since.
I recently started using conventional deadlift as an assistance exercise and it felt pretty strong, so after about two weeks, I decided to find my max conventional pull. It's the same as my sumo max. I haven't gone over about 75% on conventional deadlift in nearly a year, so I'm going to stick with it. It feels much more natural than sumo even though I think I look more like a sumo deadlifter (shorts limbs, etc).
The thing is, I'm not sure what caused such a dramatic increase in my conventional pull without training it. I definitely think good-mornings played a big part. Could sumo deadlift have increased my strength off the floor in conventional? My squat has also improved alot since then. Maybe the increased leg strength from that carries over?
In any case, I'm going to continue using both sumo and conventional in trianing.