new PR

Im a bb'er and usually im not concerned with any one rep maxes, but yesterday i wanted to see what my max was on deadlift. Over the past 4 months ive just been going up to 405 repin it out, but i felt really good, so i put on 500lbs, yes the 2.5 on each side, i couldnt resist. Anyways i pulled a double to my surprise. My w/o partner talked me into trying 545. Again, to my surprise i pulled it. Over the next 4-6 weeks im going to work on my explosive power from the beginning of the movement, and try to perfect my form. At that point im going to go for 585, if all gos well i'll shoot for 600.
The question i want to ask is how many sets and reps do you do before going for PR? When i pulled 545 i had already done 4 sets of around 25-30 reps. Again, im not a powerlifter, nor do i train like one.