Regarding #1, I did this and it seemed to really help me. Like Symmetry said in another thread, I had been going slow out of fear that going fast would result in some sort of uncontrollable movement and cause an injury. Since then, I've been pulling my warmups pretty explosively and my work sets seem to feel much easier. I think part of it comes down to just greasing that movement pattern so that it's as natural as running-- one isn't afraid to sprint out of fear that they may trip.
My last work set was also at 340 for 6 reps, 5'10, BW 170, so we're in a similar place.