How did you back injury occur? I have a torn l5s1, been dealing with it for a few years now. After what felt like some close calls I quit pulling conventional. I had worked up to a max of 600, which was a struggle. Since then I had not pulled over 500 conventional. My sumo training really took off. Well, here is a "rookie mistake for you (which turned out to be the smartest idea). I was doing my squat & dead openers two weeks out from my first meet. Well, I went to pull 575 (projected opener) and it didn't budge. Frustrated, I switched to conventional. 405,455,500,545,575 all SPEED pulls.. Two weeks later on my third attempt I pulled 640. What I am getting at is, I think sumos have a huge carryover to conventional but not vice versa. Front squats have really brough my conventional up too. Good luck!